Overview
Since the other guides are missing info, I will add info I acquire in the game so I can remember and at the same time I am sharing so other people have access too.
Mini-boss Info
Pathways possible :
You can only go underground if you start at the Sea ( automatically ) or if you go on Land and on the second map of the initial land area you use the key to open the path to the Underground ( Only available on the second map of the initial land area ).
If you are Underground as long as you aren’t in the Forge you can go back to the upper part again.
If you start on Sky you can never go Underground. If you are on land after the second map of the first land area you can never go Underground on that run too.
If you start on Sky or Sea you skip the first underground or land area. So you are effectively trading the 2-hp Mini-Boss Artifact for the 20% protection against drop / steal artifact if you plan to kill the bosses.
Sea / Underground areas are really good to get coins because you can access the secret walls without keys and then you can also use the keys to open chests meaning you can get a lot more coins / money for items.
I don’t yet know how to access the Sky Area secret areas, they definitely exist, but I can’t seem to ever be able to reach them or find a way to reach them. I think it must be related to the Rainbow Coins I found sometimes, but I was never able to use them. More info would be appreciated.
Land / Mountain area secrets can be accessed with Keys, they can be spotted if you have a key and hang into the pillars / trees that are odd. Some secret area trees are behind key walls, so you will have to use the key to open the wall and be happy that you got at least a chest instead of nothing.
Boss Info / Drops :
You can fight the Dragon at the Sky or you can fight the Pirate King at the Sea.
They will give the Gold Mask, it provides 20% protection against drops or steals.
The Dragon is a tough ( 30hp ) monster that can buff his attack / speed and has a good attack that buffs his own attack at the cost of speed, he also can apply shields on himself.
The Pirate King is a tough ( 30hp ) monster that can place debuffs that deal will deal big damage after some time, he can cast it really fast and he also applies shield on himself, so be prepared to lose some hp and have heals / shields available.
You can fight Mega Echo at the First Land area or fight Pixie at the first Underground area as their mini-bosses.
If you defeat any of them, you will get the Gold *something Artifact, it gives +2 max hp which is very useful since you usually start with 10 max hp and there aren’t many good ways of increasing it.
Mega Echo is a 25hp monster that applies regen buff over himself, or poisons you, he also has a buff that makes you receive damage everytime you hit him. So against him you want to have huge damage / stacked damage coins so you can kill him without taking too much damage. You also have to plan against his poison / regen. ( Props to you if you buff yourself before going into the fight by fighting against other enemies on the map, if you start with the damage buff coins already available you can kill him in 2-3 turns doing 10+ damage each turn very easily ).
The Pixie is a 40hp monster that fights by stealing coins, giving you a random cast coin and placing debuffs that will make you give coins to Pixie per beat. You want to kill her as fast as possible, she usually won’t be able to do much damage since any damage coins she gets will probably come from you. Remember that because she is based on stealing coins, if you defeat her you are able to get most of them back as drops from her. But she will definitely damage your deck building and it might take a while to recover. As usual try to buff yourself using some normal enemy before going into that fight.
Gold Crown gives “+1 Coins from Chest”