Overview
Legendary Achievements.
Introduction
Before we dive into the thick of things, I’d like to give a very broad advice if you want to unlock most achievements with ease: Do Everything. Every Mission, every Assignment, explore every planet, talk to every NPC, exhaust every dialogue option, kill every enemy.
There are several reasons as to why. First, some achievements actually require you to complete most missions in a specific game (e.g.”Completionist” in Mass Effect or “Master and Commander” in Mass Efect 3). Second, a good chunk of achievements are really straightforward and will unlock without you even realising it as long as you don’t skip anything. Not all of them are though. Several of them rascals are not only missable but also quite tricky so make sure to Ctrl+F “Missable” to look them up beforehand. And last but not least, because the games and their stories are incredible and worth experiencing.
A note on spoilers. Although I’ll try to avoid them as much as possible and mark them as such when I can’t, this ultimately won’t be possible for several of the achievements. If you’ve never played Mass Effect before and you really don’t want any parts of the story ruined, I would advise to finish the trilogy before going over this guide for any achievements you’ve missed.
Finally, remember to save often. These are rich and complex games. Although I’ll try my best, I probably won’t be able to cover every single outcome of every single situation and things may go wrong for you, or bugs may occur, potentially preventing you from unlocking certain achievements. If that ever happens, either you’ll be able to load a previous save or you’ll have to unlock them in another playthrough.
So, without further ado, welcome to the Mass Effect Legendary Edition 100% Achievement Guide.
Legendary Edition
Although most achievements are specific to their respective games, eleven of them span the entire trilogy.
Complete Mass Effect 1, 2 or 3 on Insanity without changing difficulty
Complete two games in Mass Effect Legendary Edition on Insanity without changing difficulty
Complete all three games in Mass Effect Legendary Edition on Insanity without changing difficulty
There are two ways to go about doing these. First, you can choose to go for a single playthrough on “Insanity” from the get go. Be aware that this will be a serious challenge. I’d recommend this method to players who have already played through the trilogy before and/or to people who don’t want to play through all three games twice.
Or, and I’d recommend this to new players of the series, you can start on an easier difficulty to get accustomed to the games and unlock a majority of the achievements and then play through the games a second time on “Insanity”. Considering you’d have unlocked most achievements the first time around, you’d be able to rush through the main storyline. Starting the second playthrough on New Game+ would also simplify things to an extent.
The choice is yours.
Mass Effect 2 will be the harder of the three games to finish on Insanity. Picking a class who has access to the power “Barrier” is recommended but not mandatory.
Finish Mass Effect 1, 2 and 3 with the same character
I’ll throw this one in here as it’s related to finishing all three games. When starting Mass Effect 2, make sure to import your character from Mass Effect instead of creating a new one. Do it again when starting Mass Effect 3.
An important part of the Mass Effect games are the romance substories. In each game, you’ll be able to chose and get close to one of several characters which will lead to a steamy scene, usually happening before the last mission or two.
Unlocking this scene is fairly easy, simply make sure to talk to whoever you want to romance most after every mission to check if they have any new available dialogue option. During said conversation, you’ll want to chose the Paragon (blue) dialogue option if available which often leads you to say something nice and any dialogue option which sounds like flirting.
If you pursue several of them at the same time, they will eventually confront you and ask you to choose. In Mass Effect 2, completing the loyalty mission of your chosen love interest is required.
Establish a romantic relationship in Mass Effect 1, 2 or 3
Mass Effect has three romanceable characters.
- Male Shepard can romance Ashley.
- Female Shepard can romance Kaidan.
- Both of them can romance Liara.
Spoilers
During the mission on Virmire, you’ll be faced with a choice to either assist Ashley or Kaidan once Saren attacks. If you have your heart set on romancing either of these characters, make sure to assist said character as the other one will get killed.
Establish or rekindle a romantic relationship in two games in Mass Effect Legendary Edition
Mass Effect 2 has six romanceable characters for the purpose of unlocking the achievement.
- Female Shepard can romance Garrus, Jacob and Thane.
- Male Shepard can romance Jack, Miranda and Tali.
(A spoiler-ish note about Jack: Do not agree to the no strings attached, one night stand with her early on as this will prevent you from having a proper romance with her later on and thus unlocking the achievement.)
(If you import your Mass Effect save in which you romanced Liara, you can continue said romance as part of the “Lair of the Shadow Broker” DLC. However, this will not unlock the Paramour achievement. The same limitation applies to three other romantic interests which are Kelly Chambers, Morinth and Samara. If you do decide to romance Morinth, be careful. She… bites.)
Establish or rekindle a romantic relationship in all three games in Mass Effect Legendary Edition
Mass Effect 3 has ten romanceable characters for the purpose of unlocking the achievement.
- Female Shepard can establish a romance with Samantha. Romance with Garrus can only be rekindled from Mass Effect 2.
- Male Shepard can establish a romance with Ashley and Steve. Romances with Jack, Miranda and Tali can only be rekindled from Mass Effect 2.
- Both of them can establish a romance with Kaidan and Liara. Romance with Kelly can only be rekindled from Mass Effect 2.
(Five more characters can be romanced (albeit in a different, usually toned down way). However, they will not unlock the Paramour Achievement. They are James and Javik for female Shepard. Thane is also available only if continued from Mass Effect 2. Diana can be romanced by both as well as Samara but only if continued from Mass Effect 2.)
For additional information about Romances, check the wiki page on the subject as it wouldn’t be sensible or useful to cover everything in this guide.
[link]
Kill 250 enemies in Mass Effect 1, 2 or 3
Kill 1,000 enemies in Mass Effect 1, 2 or 3
Kill 2,000 enemies in Mass Effect 1, 2 or 3
I personally wouldn’t sweat too much about farming these as there should be enough enemies in all three games to reach 2,000 kills in a single playthrough as long as you don’t rush through the main storyline (which you shouldn’t do anyway).
Kill 100 enemies with melee attacks in Mass Effect 1, 2 or 3
This one might be a little bit more tricky however, especially if you’re playing on “Insanity” or if you’re playing a class focused on long ranged combat. Although I would still try to get as many melee kills as possible during the entire playthrough (Husks and Varrens are particularly good targets), you may want to hold off on them until you reach Mass Effect 3. As part of the Citadel DLC, a combat simulator was introduced allowing the player to fight enemies in a controlled environment.
Mass Effect
ME1: Complete the majority of the game
The majority here means completing 50 Missions/Assignements out of the 76 available in the game. Heed my advice to “Do Everything. Every Mission, every Assignment” and you’ll get this no problem.
Be aware however, that the game seems to have forgotten how to count and there are reports of the achievement requiring more than 50 missions to be completed before it unlocks (Somebody in the comments reported getting it after 72, I personally unlocked mine when I reached 46 missions so go figure). In that sense, the only advice I have really is to finish missions until it does.
Also, make sure you’ve unlocked this achievement before you cross the point of no return (Mission: Ilos: Find the Conduit) as you won’t be able to do anything else in the game once you do.
For more information, check the “Completionist Achievement Guide” from the wiki as it contains a complete list of all missions.
[link]└ Story
These achievements are story related and can’t be missed.
ME1: Complete Eden Prime
ME1: Become a Spectre
ME1: Locate Dr. T’soni in the Artemis Tau cluster
ME1: Complete Feros
ME1: Complete Noveria
ME1: Complete Virmire
Note: Make sure you’ve completed everything you need to before heading to Ilos (“Ilos: Find the Conduit”) as this will lock you into the end of the game.
ME1: Complete Ilos
ME1: Complete the game on any difficulty
└ Squad
These achievements are listed in more of less the order you’ll unlock the squad members needed to obtain them. With 76 Missions/Assignments in the game, you should have no problem getting all of those as long as you rotate your squad members as soon as you unlock their respective achievements.
Although unlikely, do make sure you unlock all six of them as soon as possible and before completing a majority of the Missions/Assignments as this could lock you out of getting them, especially considering the game seems to struggle counting to 5 and you may often need a couple more.
ME1: Complete 5 missions with the Alliance sentinel squad member
This refers to Kaidan Alenko. He will be the first squad member you get access to at the very beginning of the game.
ME1: Complete 5 missions with the Alliance soldier squad member
This refers to Ashley Williams. You will unlock her during the very first mission on Eden Prime. If you keep her and Kaidan in your squad for the first few missions on the Citadel, both of these achievements should unlock early on.
ME1: Complete 5 missions with the turian squad member
ME1: Complete 5 missions with the krogan squad member
ME1: Complete 5 missions with the quarian squad member
These refer to Garrus Vakarian, Urdnot Wrex and Tali’Zorah nar Rayya respectively. You’ll unlock all three of them during your first visit on the citadel, a few Missions in and before becoming a Spectre.
Spoilers
I would advise to complete 5 Missions with Wrex early on as there is a chance he dies during a mission on Virmire.
ME1: Complete 5 missions with the asari squad member
This refers to Liara T’Soni. You’ll unlock her as a squad member after you finish the mission “Find Liara T’Soni” which I’d recommend doing as soon as possible. As you strongest biotic ally, she will be very valuable in unlocking some potentially grindy achievements we’ll cover next.
└ Talents
Note: to unlock these, you can use the required powers yourself if you have access to them or order your squadmates to use theirs while the game is paused. In that regard, I recommend disabling “Squad Power Usage” in the options (until you’ve unlocked all relevant achievements at which point you should enable it again) so that their cooldowns are always available for you to activate.
As progress carries over saving and loading, you are able to farm these quickly if you so desire. Simply find a good spot, save, use the required powers and load. Rinse and repeat.
Here’s a list of who has access to what.
Biotic
Tech
ME1: Use biotic Barrier 25 times
ME1: Use biotic Lift 25 times
ME1: Use biotic Singularity 25 times
ME1: Use biotic Stasis 25 times
ME1: Use biotic Throw 25 times
ME1: Use biotic Warp 25 times
Those are the six biotic talents available to the Adept class. Liara also has access to all of them.
Except for Barrier, they all need to be used on a target to count. In this regard, enemies but also Citadel Rapid Transport terminals and the Mako count as targets if you wish for a way to farm those outside of combat.
ME1: Use AI Hacking 25 times
ME1: Use Damping Field 25 times
ME1: Use Shield Overload 25 times
ME1: Use Neural Shock 25 times
ME1: Use Sabotage 25 times
Those are the five Tech talents available to the Engineer class. Tali also has access to all of them except Neural Shock, you’ll want to bring Kaidan for this last one.
Neural Shock and AI Hacking need to be used on an actual enemy to count although targeting the Mako also work for Neural Shock, simply land on a planet and aim at it or order Kaidan to do it for you.
Damping, Overload and Sabotage do not require any target and can be used while running around the Citadel.
ME1: Use medi-gel 50 times
You can use medi-gel to heal yourself and your allies as well as revive them. If you play on “Insanity”, you shouldn’t have any problem getting this in a single playthrough. On lower difficulties, you may have to farm this at some point unless you’ve planned to play the game a second time as the progress would carry over.
└ Misc.
ME1: Find all primary Alien: Council Races, Extinct Races and Non-Council Races codex entries
Although there are several ways (except for Protheans) to unlock each of these codex entries, I will only list one of them down below (usually the earliest opportunity) to keep this guide as short as possible. Remember to “Talk to every NPC, exhaust every dialogue option”.
These are sorted in a roughly chronological order, within their subcategories. By following this list, you should be able to unlock this achievement during you first trip to the Citadel following Eden Prime.
Council Races:
- Asari, Salarian and Turian: unlocked automatically after your first meeting with the Council.
Extinct Races:
- Protheans: during a conversation with Nihlus and Captain Anderson at the very beginning of the game, before Eden Prime (“Investigate”, “Protheans”).
- Rachni: on the Citadel, access the Avina terminal (hologram) near the Krogan statue, close to the Emporium (“Investigate”, “Rachni Wars”).
Non-Council Races:
- Geth: during a conversation with Ashley after you meet her for the first time (“Investigate”, “Geth”).
- Keepers: on the citadel, access the Avina terminal located next to a Keeper, near the elevator leading to the Council Tower (“Investigate”, “Keepers”).
- Elcor and Volus: on the Citadel, find their embassy located next to the Human one. In the room, talk to ambassador Calyn (the big one (“Investigate”, “Elcor”) and ambassador Din Korlack (the small one (“Investigate”, “Volus”).
- Hanar: on the Citadel, inside the Emporium, talk to the Hanar shopkeeper (“Investigate”, “Speech”)
- Krogan – unlocked automatically when Wrex is recruited.
- Quarian – unlocked automatically when Tali is recruited.
- Batarian: right after becoming a Spectre, talk to Anderson in front of the Normandy (“You and Saren have a past”; “What happened”).
ME1: Accumulate 75% of total possible Paragon or Renegade points
Blue or Red, a classic. In Mass Effect, during various conversations, you’ll encounter Blue (top-left) and Red (bottom-left) dialogue options which relate to the Charm and Intimidate talents. Level either of them up to be able to use said options and obtain some points to either Paragon or Renegade respectively.
This isn’t the only way to earn points though. Doing and saying what you perceive to be the right thing during missions (top-right) will also earn you Paragon points. And so is being a jerk (bottom-right) for Renegade.
Paragon will lead you to be a more kind and compassionate Shepard.
Renegade will lead you to be a ruthless jerk. Also, scars.
Decide early on which kind of Shepard you want to be and you’ll get this achievement eventually. With that being said, there are enough opportunities in the game to increase your score one way or the other as long as you complete most missions so don’t be afraid to choose the opposite dialogue option once in a while if you prefer the outcome, just don’t overdo it.
Furthermore, if you’re afraid you may not be able to reach the required amount, a bug can be exploited during a mission on Noveria for virtually infinite Paragon/Renegade points. Here’s how:
Follow the natural progression of the mission “Noveria: Geth Interest” until “Noveria: Lorik Qui’in” starts. Here’s a breakdown of the latter:
- Agree to help Lorik Qui’in and get the evidence he wants.
- Gianna will wait for you outside, asking you to meet her at the bar. Do so and she’ll ask you to convince Lorik to testify.
- Talk to him, choose “Testify against Aloneis” and then choose either the Charm (“You’d be a hero”) or Intimidate (“Damn right I will”) option. (5 points required in either skill tree.)
- You’ll be rewarded with Paragon/Renegade points and the quest will advance to the next step.
- Now, in order to farm the points, talk to him again immediately. Completing the mission will prevent you from getting more.
- Choose “Matriarch Benezia” and then “Another question”. From then on, you’ll once again have access to the “Testify against Aloneis” dialogue option and the Charm/Intimidate one after that.
- Rinse and repeat until you’re satisfied with the amount or you got the achievement.
For additional information about Morality, check the wiki page on the subject as it lists every instance where you can get Paragon/Renegade points.
[link]
ME1: Use Charm or Intimidate to resolve an impossible situation
Charm and Intimidate are talents used to get people to do things they may not have wanted to do originally. Although they correspond to Paragon and Renegade respectively, they aren’t exclusive to them which means you can be a Charming Renegade if you so desire.
That being said, there are only two opportunities in the whole game to unlock this achievement and they both are key moments in the story so, spoilers-ish.
The first one is during a Mission on Virmire. Wrex will be pissed off on the subject of the genophage. He’ll storm off and start shooting at birds, go talk to him. This is when you’ll need to use the Charm/Intimidate (8 points required in either skill tree) option to defuse the situation and get the achievement. (If you complete “Wrex: Family Armor” before going to Virmire, you won’t need the 8 points in the skill tree but have access to the Charm/Intimidate options regardless and still get the achievement.) There is a way Wrex gets killed during this scene so save before and be mindful of your dialogue choices.
The other is at the very end of the game, during the final mission. Avoiding spoilers, just keep an eye out for three different Charm/Intimidate dialogue options happening one after the other during a key conversation (12 points required in either skill tree). Choose all three of them.
Before a fight even begins, you’ll have a conversation with Saren. Choose the Charm/Intimidate options whenever they appear on the left. If successful, he will shoot himself and spare you the first of two fights with him.
ME1: Land on an uncharted world
ME1: Land on 4 uncharted worlds
ME1: Land on 8 uncharted worlds
Uncharted worlds refer to planets you can land on and drive around in the Mako. Main missions planets such as Feros don’t count. You should get these naturally by completing assignments but if you want to unlock these quickly, landing on the same planet eight times will count and unlock all three achievements.
ME1: Complete the Bring Down the Sky mission.
This achievement is story-related and will unlock at the end of the Bring Down the Sky DLC. It can’t be missed as long as you play through it. You need to do so before “Ilos: Find the Conduit”. (Mission X57: Bring Down the Sky, head to Asteroid X57 located in the Asgard System in the Exodus Cluster.)
Mass Effect 2
For the love of everything you hold dear, save often. Several missions can go ways you don’t want to when it comes to getting every achievement so you’ll love being able to load and try again.
Also, this is the first time of many I’m going to say this and I won’t go into details here but keep in mind that you should complete loyalty missions as early as possible.
Focusing on either Paragon or Renegade from the beginning instead of doing a bit of both will potentially save you some trouble later on.
└ Story
These achievements are story related and except for three of them, they can’t be missed.
ME2: Save your crew from an overwhelming attack
ME2: Return to active duty
ME2: Successfully recruit Archangel
Unlocked by completing the mission “Dossier: The Archangel”.
ME2: Successfully recruit the biotic Convict
Unlocked by completing the mission “Dossier: The Convict”.
ME2: Successfully recruit the krogan
Unlocked by completing the mission “Dossier: The Warlord”.
ME2: Successfully recruit the Professor
Unlocked by completing the mission “Dossier: The Professor”.
ME2: Defend a human colony from attack
Unlocked by completing the mission “Horizon”.
ME2: Successfully recruit the Assassin
Unlocked by completing the mission “Dossier: The Assassin”.
ME2: Successfully recruit the Justicar
Unlocked by completing the mission “Dossier: The Justicar”.
ME2: Successfully recruit the quarian
Unlocked by completing the mission “Dossier: The Quarian”.
ME2: Complete the investigation of a derelict alien vessel
Unlocked by completing the mission “Collector Ship”.
Warning: Make sure you’ve completed everything you need to (Loyalty Missions, Ship Upgrades (covered under “No One Left Behind”, don’t skip this), grind, etc.) before starting this next mission (“Reaper IFF”) as a countdown should begin soon after you complete it and things will happen to the Normandy’s Crew if you delay it (which shouldn’t prevent you from getting the achievement but the way they die is quite gruesome). Delay here means doing any other Mission or Assignment instead of going through the Omega 4 Relay. There is a possible grace period of a couple Missions but the way the game decides it is apparently iffy so I wouldn’t count on it. This is extremely important for the following achievements.
ME2: Obtain geth technology
At the end of the mission “Reaper IFF”, keep the captured Geth by deciding to go talk to it when faced with a choice to give him to Cerberus.
You should activate him immediately and do his loyalty mission first thing after that mission.
ME2: Use the Omega 4 Relay
ME2: Survive suicide mission
I marked this as missable but you’d actually have to try and do the complete opposite of what needs to be done for the next achievement to not unlock it so don’t sweat it.
ME2: Keep your team alive through the suicide mission
Alright, this is it. This is the big one. Save before this mission just in case something goes wrong.
First and foremost, you need to install all three available Normandy upgrades BEFORE you go through the Omega 4 relay.
- Tali provides the Multicore Shielding.
- Jacob provides the Heavy Ship Armor.
- Garrus provides the Thanix Cannon.
If you forget any of these people are going to die before you even reach your destination, thus locking you out of the achievement.
This is where all those loyalty missions you’ve completed are going to become useful. If you didn’t finish some of them, characters for whom you didn’t are more likely to die.
Note: During the course of the game, two confrontations are going to happen at some point after you complete their respective loyalty missions. The first one between Jack and Miranda, the other between Legion and Tali. In order to NOT have to side with either of them and therefore lose their loyalty, you will need enough Paragon or Renegade points to have access to either the Charm or Intimidate dialogue options. If for some reasons you don’t have access to said options because your points are too low, you’ll be able to talk to the character you didn’t side with once you do have enough points to make them loyal again.
Now, for the most important part: who goes where. Although there are several ways to go about this, the list down below has been proven to work. Let me know in the comment if it didn’t for you and we’ll try and figure it out.
Collector Base Infiltration:
- Tech Specialist: choose Legion only if you had time to do his loyalty mission, otherwise choose Tali or Kasumi.
- Diversion Squad Leader: choose Garrus (Jacob and Miranda would also be fine).
The Long Walk
- Biotic Specialist: choose Samara/Morinth (Jack would also be fine).
- Second Team: choose Garrus (Jacob and Miranda would also be fine).
- Escort for Survivors: choose Mordin.
When it comes time to choose your personal squad for the final part, you should take “weaker” characters such as Tali, Kasumi and Jack and let “tankier” ones like Grunt, Zaeed and Thane hold the line.
Now, I’m going to sound like a broken record but if you made sure to complete everybody’s loyalty mission, the defensive score of the group holding the line should be high enough for a perfect mission worthy of the achievement’s name.
Good luck.
ME2: Save humanity throughout the galaxy from certain annihilation
You’ve finished the game, congratulations.
└ Loyalty Missions
Reminder: During the course of the game, two confrontations are going to happen at some point after you complete their respective loyalty missions. The first one between Jack and Miranda, the other between Legion and Tali. In order to NOT have to side with either of them and therefore lose their loyalty, you will need enough Paragon or Renegade points to have access to either the Charm or Intimidate dialogue options. If for some reasons you don’t have access to said options because your points are too low, you’ll be able to talk to the character you didn’t side with once you do have enough points to make them loyal again. I’d still recommend to push said loyalty missions for last, when your Paragon/Renegade is high enough.
ME2: Hack a geth collective
This refers to Legion (“Legion: A House Divided”). I already covered it above but just in case, at the end of the “Reaper IFF” mission, choose to talk to it in order to keep it. The first thing you do right after that should be to talk to him again on your ship to unlock his loyalty mission.
This should also decidedly be the last loyalty mission related achievement you get. Remember what I said earlier about doing every loyalty mission before you even think of starting “Reaper IFF”.
ME2: Gain the loyalty of the krogan
This refers to Grunt (“Grunt: Rite of Passage”).
Although not a loyalty mission achievement per say, this next one can be unlocked at the end of the aforementioned mission.
Big Game Hunter (Missable) ME2: Thresher Maw defeated This is marked as missable because you do not need to kill it in order to finish the mission, only to survive it. Well, you’re going to kill it anyway. Armor piercing ammo and Incendiary ammo will be useful as its health is entirely armor. Good Luck. 
ME2: Gain the loyalty of the thief
This refers to Kasumi (“Kasumi: Stealing Memory”).
ME2: Gain the loyalty of the biotic Convict
This refers to Jack (“Jack: Subject Zero”).
ME2: Gain the loyalty of the Assassin
This refers to Thane (“Thane: Sins of the Father”).
It is possible to fail at earning Thane’s loyalty. Make sure to save beforehand.
In order to succeed, you’ll need to prevent Thane’s son from assassinating his target (either by preventing the death or killing the target yourself through the Renegade interruption).
ME2: Help the Justicar resolve her mission
This refers to Samara (“Samara: The Ardat-Yakshi”).
It is possible to fail at earning Samara’s loyalty. Make sure to save beforehand.
Honestly, this mission is tricky enough and overall a pain in the ass I’ll just link the wiki page on the subject for now. I’ll probably revisit this later, once I’ve replayed through it and believe I can explain it properly.
[link]
ME2: Gain the loyalty of Archangel
This refers to Garrus (“Garrus: Eye for an Eye”).
ME2: Gain the loyalty of the Cerberus Operative
The refers to Jacob (“Jacob: The Gift of Greatness”).
ME2: Gain the loyalty of the mercenary
This refers to Zaeed (“Zaeed: The Price of Revenge”).
It is possible to fail at earning Zaeed’s loyalty. Make sure to save beforehand.
In order to succeed, you will have to follow the Renegade path when comes time to decide whether or not to save the workers. If you do decide to go Paragon and save the workers, you will have one last chance to gain his loyalty at the end of the mission but it will require a high-level Charm decision, only available if your Paragon is high enough. Remember to save beforehand if you want to attempt the latter.
ME2: Gain the loyalty of the Professor
This refers to Mordin (“Mordin: Old Blood”).
ME2: Gain the loyalty of the Cerberus Officer
This refers to Miranda (“Miranda: The Prodigal”).
ME2: Gain the loyalty of the quarian
This refers to Tali (“Tali: Treason”).
It is possible to fail at earning Tali’s loyalty. Make sure to save beforehand.
In order to succeed, respect her wishes to not provide the evidence that her father was guilty during the trial.
└ Combat
ME2: Perform 30 headshot kills with any weapon on humanoid targets
You should get this naturally by playing the game, just aim for the head. Humanoid refers to anything that looks like a human, including robots as long as they walk on two legs.
ME2: Make 20 enemies scream as they fall or are set on fire
Literally every power, be it tech, biotic or plain ammo, that can send enemies flying or set them on fire will count for this. You should get this in no time without even trying.
Reminder: to unlock these, you can use the required powers yourself if you have access to them or order your squadmates to use theirs while the game is paused. In that regard, I recommend disabling “Squad Power Usage” in the options (until you’ve unlocked all relevant achievements at which point you should enable it again) so that their cooldowns are always available for you to activate.
As progress carries over saving and loading, you are able to farm these quickly if you so desire. Simply find a good spot, save, use the required powers and load. Rinse and repeat.
Here’s a list of who has access to what.
ME2: Incinerate the armor of 25 enemies
The Incinerate ability is required for this achievement. Whenever you encounter an enemy with armor, you should try shooting them a bit to lower said armor, especially on “Insanity”, before using Incinerate. This is because the power needs to remove the entirety of what’s left of the armor for it to count.
ME2: Disrupt the shields of 25 enemies
The Overload ability is required for this achievement. Whenever you encounter an enemy with a shield, you should try shooting them a bit to lower said shield, especially on “Insanity”, before using Overload. This is because the power needs to remove the entirety of what’s left of the shield for it to count.
ME2: Warp the barriers of 25 enemies
The Warp ability is required for this achievement. Whenever you encounter an enemy with a barrier, you should try shooting them a bit to lower said barrier, especially on “Insanity”, before using Warp. This is because the power needs to remove the entirety of what’s left of the barrier for it to count.
ME2: Hit 20 different targets with multiple biotic powers to combine the effects
Although not necessary, this will be easier if you chose a class with biotic powers. Regardless, the simplest way to get this is to use or order one of your squadmates to Lift or Pull an enemy and then use or order somebody else to hit it with any other biotic power such as Warp or Throw. Characters with access to biotic talents are Miranda, Jacob, Thane and Jack.
This does not seem to work if you, the player, use both powers. You need to use one and order a squadmate to use the other. Quite a few people report this achievement to be finicky in how it counts progress so I would advise grinding this as early as possible.
└ Misc.
ME2: Complete a mission discovered by scanning an unexplored world
ME2: Complete 5 missions discovered by scanning unexplored worlds
While scanning planets for resources, some of them will be marked as anomalies. Scan them to find the right spot and launch a probe. Once that’s done, land on the planet and complete the mission. Here’s a list of all possible missions based on where they’re found.
ME2: Visit 100% of the planets in an unexplored cluster
When in a specific cluster, a percentage will be displayed in the top-left corner. Simply “visit” (click on) every planet until you reach 100%.
ME2: Unlock 15 new Mass Effect 2 codex entries
This will come naturally as you play through the game. Make sure to talk to everybody, as usual.
ME2: Complete any research project in the Normandy’s laboratory
What is says on the tin. Go to the tech lab on the Normandy (unlocked after recruiting Mordin), choose an upgrade and research it.
ME2: Evolve any power
In order to evolve a power, you’ll first need to level up one of them to the maximum which requires ten skill points. Once done, a message will pop up asking you to make a choice.
ME2: Fully upgrade a weapon
You will find various weapon upgrades across many missions and in stores. Many of them are easily missable so make sure to look everywhere and try to focus on a single weapon to acquire this achievement as early as possible.
For the complete list of upgrades, the wiki is your best friend. This will allow you to focus on a single weapon and not have to waste time getting all of them if you don’t wish to.
[link]
ME2: Successfully shut down the rogue VI in Project Overlord
This achievement is story-related and will unlock towards the end of the Overlord DLC, after the final boss fight. It can’t be missed as long as you play through it. (Mission “Overlord”, available after you receive a message on your terminal from the Illusive Man.)
To start the mission, look for “Investigate Project Overlord” on the galaxy map.
ME2: Confront the Shadow Broker
This achievement is story-related and will unlock towards the end of the Lair of the Shadow Broker DLC, before the final boss fight. It can’t be missed as long as you play through it. (Mission “Lair of the Shadow Broker”, available after you receive a message on your terminal from Cerberus Information Processing.)
To start the mission, look for “Give Liara Intel” on the galaxy map.
Mass Effect 3
A point about Missions: you should focus on completing side missions as soon as they are available and before the main ones (usually marked as Priority:). This is because some side missions can basically fail and become impossible to do if you go too far in the main storyline, thus preventing you from unlocking the associated achievements. I’ll go over them in more details in the Story section but early warnings can’t hurt.
ME3: Deliver most of the Galaxy at War assets to the final conflict
In the original game, you needed your Effective Military Strength at 4,000 before starting the invasion of the Cerberus HQ. This is yet to be confirmed for the Legendary Edition, especially considering multiplayer is not is this version despite being required in the original.
I’ve seen reports that 5600 may be the new score to obtain, to be confirmed.
I’ll probably go into more details later but the gist of it is, you’ll be fine if you’ve done the vast majority of missions available in all three games up to this point.
└ Story
These achievements are story related and can’t be missed. However, some side missions CAN be missed if they are not completed before some of the “Priority:” ones, I’ll cover them individually.
ME3: Return to active duty
ME3: Chase down an assassin
ME3: Bring a veteran officer aboard
ME3: Explore a lost city
Unlocked by completing the mission “Priority: Tuchanka”.
Warning: You must complete the sidequest “Attican Traverse: Krogan Team” BEFORE the Mission “Priority: Tuchanka” to not get locked out of the achievement “Tunnel Rat”.
Tunnel Rat (Missable) ME3: Survive the swarm Unlocked by completing the mission “Attican Traverse: Krogan Team”. 
ME3: Win a political stand-off
Unlocked by completing the mission “Priority: Citadel II”.
Warning: You must complete the sidequest “Grissom Academy: Emergency Evacuation”‘ BEFORE the Mission “Priority: Citadel II” to not get locked out of the achievement “Liberator”.
Liberator (Missable) ME3: Stop a Cerberus kidnapping Unlocked by completing the mission “Grissom Academy: Emergency Evacuation”. 
ME3: Evacuate a scientific facility
Unlocked by completing the mission “Arrae: Ex-Cerberus Scientists”.
Although not a Story mission per say, I’ll throw this one in here anyway because you unlock it right after “Priority: Citadel II” and because you could in theory miss this achievement if you ignore the mission altogether. They will reward you with War Assets too (“Master and Commander”).
ME3: Sabotage a dreadnought
Unlocked by completing the mission “Priority: Geth Dreadnought”.
ME3: Call down an orbital strike
Unlocked by completing the mission “Priority: Rannoch”.
Warning: You must complete the sidequest “Rannoch: Geth Fighter Squadrons”‘ BEFORE the Mission “Priority: Rannoch” to not get locked out of the achievement “Saboteur”.
Saboteur (Missable) ME3: Disable a group of fighter squadrons Unlocked by completing the mission “Rannoch: Geth Fighter Squadrons”. 
ME3: Extract ancient technology
Unlocked by completing the mission “Priority: Thessia”.
Warning: You must complete the sidequest “Kallini: Ardat-Yakshi Monastery”‘ BEFORE the Mission “Priority: Thessia” to not get locked out of the achievement “Fact Finder”.
Fact Finder (Missable) ME3: Discover an enemy’s monstrous origin Unlocked by completing the mission “Kallini: Ardat-Yakshi Monastery”.
ME3: Send a warning across the galaxy
Unlocked by completing the mission “Priority: Horizon”.
Remember to complete everything you want before this point as you won’t be able to after starting this next Mission.
ME3: Defeat an old adversary
Unlocked by completing the mission “Priority: Cerberus Headquarters”.
ME3: Make the final assault
Unlocked by completing the mission “Priority: Earth”.
ME3: Mission accomplished
You’ve finished the game, congratulations.
└ Combat
ME3: Kill a brute while it’s charging you
Pretty straightforward. You’ll get many opportunities to achieve this during the course of the game. Lower its health and wait for it to charge to make it easier.
ME3: Defeat a harvester
Pretty straightforward. You’ll get many opportunities to achieve this during the course of the game and is effectively unmissable.
ME3: Destroy an Atlas dropped from orbit
Pretty straightforward. You’ll get many opportunities to achieve this during the course of the game and is effectively unmissable (e.g. you will encounter one during the main mission “Priority: Sur’Kesh”).
ME3: Hijack an Atlas mech
Not so straightforward. Same enemy as above. This time though, you’ll want to focus your firepower on the orange glass part to break it and then kill the pilot. A sniper rifle is recommended but not mandatory. If the mech hasn’t been destroyed, you’ll be able to approach it and take control of it.
The mech will automatically explode if it is the last enemy you kill during a fight so make sure to keep anybody else alive before attempting the method above.
Reminder: to unlock these, you can use the required powers yourself if you have access to them or order your squadmates to use theirs while the game is paused. In that regard, I recommend disabling “Squad Power Usage” in the options (until you’ve unlocked all relevant achievements at which point you should enable it again) so that their cooldowns are always available for you to activate.
As progress carries over saving and loading, you are able to farm these quickly if you so desire. Simply find a good spot, save, use the required powers and load. Rinse and repeat.
ME3: Set 100 enemies on fire with powers
Inferno ammo, Incinerate, Inferno grenades and everything else that can set enemies on fire will count for this achievement.
ME3: Lift 100 enemies off the ground with powers
Lift, Throw, Pull, Concussion Shot, Lift Grenade and everything else that can send your enemies flying will work.
This achievement appears to be buggy in the sense that your squadmates’ uses will not count. In that regard, if you’re playing a class without any of the required powers, you will be able to acquire two new ones by completing the Omega DLC. Once you have, go to the medbay in the Normandy and choose either Flare or Lash as your bonus power.
ME3: Overload the shields of 100 enemies
The Overload ability is required for this achievement. Unlike Mass Effect 2, you do not need to deplete the entire shield for it to count, simply use the power on any enemy with a shield. The Engineer/Sentinel have access to it as well as EDI, Garrus and Kaidan.
ME3: Perform any combination of 50 biotic combos or tech bursts
Same advice as “Tactician” from Mass Effect 2 except now you can use tech skills as well as biotic ones to combo.
ME3: Kill 10 guardians with headshots from the front while their shields are raised
Guardians are the enemies hiding behind a shield as big as them. You’ll need to kill ten of them by shooting in the tiny hole they look through. Using a sniper is advised.
└ Misc.
ME3: Escape a Reaper in the galaxy map
You should get this by yourself early on but just in case, in occupied systems, indicated by a Reaper on top, scanning will alert them of your presence represented by a progress bar in the bottom-left corner. Keep scanning until they attack you. You’ll unlock this once you escape the system by going through the mass relay or fly past the border.
ME3: Dispatch 10 probes to retrieve people or resources in Reaper territory
Same as above. Go into Reaper territory and scan planets until you find something interesting and send a probe. Be mindful not to scan too much and alert the Reapers.
ME3: Visit a store on the Citadel
I’m Commander Shepard and this is my favorite store on the Citadel.
ME3: Obtain two non-customizable suits of armor
In various shops across the game, you’ll find full body sets of armor (as opposed to armor for specific body parts) selling for 50,000 Credits or on the Normandy for 55,000. Buy two of them and this will pop.
ME3: Evolve any of your powers to rank 6
You should get this naturally honestly, just focus on a single power and you’ll be fine.
ME3: Modify a weapon
Equip any mod on any weapon. Ding!
ME3: Upgrade any weapon to level 10
This achievement stands unique in this list as it will require you to start a New Game+ Mass Effect 3 save (to do so, start a new game and import your first character). Indeed, during your first playthrough, you will only be able to upgrade your weapons up to level 5.
Make sure to level up as many weapons as you can during your first playthrough, just in case, but the main recommendations would be the M8 Avenger and the M3 Predator as you will acquire them during the very first mission of the game. (For weapons you need to find in the game as opposed to the ones you can buy in stores, their level will be locked at 7 until you find them a second time during the second playthrough, making the ones mentioned good candidates.)
You should also not waste your credits during your first playthrough as they will carry over to your second.
Once you’re back on the Normandy during your second playthrough, head to the Upgrade Terminal, you should be able to level either of these weapons to level 10 granted you have the credits.
For a complete list of weapons present in the game, the wiki is your friend.
[link]
ME3: Uncover an ancient secret
This achievement is story-related and will unlock at the end of the Leviathan DLC. It can’t be missed as long as you play through it. (Mission “Citadel: Dr. Bryson”, available after you receive a message on your terminal titled “Urgent message from Admiral Hackett”).
To start the mission, look for “Meet Dr. Bryson” on the galaxy map.
ME3: Free Omega from Cerberus Occupation
This achievement is story-related and will unlock at the end of the Omega DLC. It can’t be missed as long as you play through it. (Mission “Citadel: Aria T’Loak”, available after you receive a message on your terminal from Aria T’Loak titled “Omega: It’s time”).
ME3: Stop an out-of-control scheme before it’s too late
This achievement is story-related and will unlock at the end of the Citadel DLC. It can’t be missed as long as you play through it. (Mission “Citadel: Shore Leave”, available after you receive a message on your terminal from Admiral Hackett titled “Priority: Citadel Shore Leave”).
ME3: Defeat a group of Spectre-level opponents on Normal, Hardcore, or Insanity
First, you’ll need to purchase the “Mirror Match” at the Armax Store. Then, go into the combat area and choose said “Mirror Match”. Good luck, I don’t really have any advice yet (never actually done it), just try not to die.
Closing Remarks
Thank you to everybody who may have contributed to the Mass Effect wiki which has been invaluable in writing this guide and is overall a treasure trove of information about the trilogy.
[link]Thank you to everybody down in the comments who contributed to the guide by correcting or confirming parts of it. It is much better thanks to you.
Wallpaper/Icons come from the official fan art pack provided by Bioware.
Screenshots are my own.
If I forgot anything or made any mistakes, or if anything isn’t clear, please let me know in the comments.
If you found this guide useful, consider rating it and putting it in your favorites. This will allow you to quickly access it in-game from the Steam overlay.
And finally, thank you for reading!