Recommended level for every boss and their affinities. No spoilers

First boss of game Shadow Yosuke
Very easy fight. you should try to be at level 1-2.

Phys-
Fire -
Ice -
Elec - Weak
Wind -
Light - Null
Dark - Null
Almi -

First boss of dungeon Shadow Chie Floor 2
This boss is pretty easy, you should be fine any level.

Phys - Strong
Fire -
Ice -
Elec -
Wind - Weak
Light - Null
Dark - Null
Almi -


Second boss of dungeon Avenger Knight Floor 5
This is the first real mini boss of the game. You should be around level 7-8.

Phys -
Fire - Weak
Ice -
Elec -
Wind -
Light -Null
Dark - Null
Almi -


Final boss of dungeon Shadow Yukiko Floor 8
You should be around Level 13-15 for this fight.

Boss Summon - Prince Charming: Weak to Elec
Phys -
Fire - Drain
Ice - Weak
Elec -
Wind -
Light - Null
Dark - Null
Almi -


Optional boss for dungeon Contrarian King Floor 8
This is the first Optional of the game. You should try to be around level 18-20. Come prepared with buffs/debuffs as there are no weaknesses to utilize. If it's too difficult, you can always come back later.

Phys -
Fire - Drain
Ice -
Elec -
Wind - Null
Light - Null
Dark - Null
Almi - Strong

Only mini boss of dungeon Daring Gigas Floor 7
For this fight you'll want to be around level 22-23.

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Final boss of dungeon Shadow Kanji Floor 11
For this fight I would recommend being around 25-27.

Final Boss of dungeon Shadow Kanji
Phys -
Fire -
Ice -
Elec - Drain
Wind -
Light - Null
Dark - Null
Almi -

Boss Summon 1 - Nice Guy
Phys -
Fire - Null
Ice - Weak
Elec -
Wind - Strong
Light - Null
Dark - Null
Almi -

Boss Summon 2 - Tough Guy
Phys -
Fire - Weak
Ice - Null
Elec -
Wind - Strong
Light - Null
Dark - Null
Almi -

Optional boss of dungeon Intolerant Officer Floor 11
Try to be around level 27-29

Phys -
Fire -
Ice - Weak
Elec - Weak
Wind - Weak
Light - Null
Dark - Null
Almi - Strong

Only mini boss of dungeon Amorous Snake Floor 7
This fight you want to be around level 29-30.

Phys -
Fire - Weak
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Final boss of dungeon Shadow Rise/Shadow Teddie Floor 11
This fight try to be around 30-33.

Phase One Shadow Rise
Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Phase two Shadow Teddie
Phys -
Fire -
Ice - Drain
Elec -
Wind -
Light - Null
Dark - Null
Almi - Strong

Optional boss Momentary Child Floor 11
This is a pretty easy fight, try to be around 32-35.

Phys -
Fire -
Ice - Weak
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Only mini boss of dungeon Killing Hand Floor 7
Try to be around 34-37.

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Final boss of dungeon. Shadow Mitsuo Floor 10
For this fight try to be around 40-43

Phys - Strong
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Optional boss Escapist Soldier Floor 10
This fight you'll want to be around 45-46.

Phys - Strong
Fire -
Ice - Weak (No knockdown, takes 125% more damage)
Elec -
Wind - Weak (No knockdown, takes 125% more damage)
Light - Null
Dark - Null
Almi - Strong

Only mini boss of dungeon Dominating Machine Floor 4
Try to be around level 48-50.

Phys - Strong (Reduced 75%)
Fire - Strong (Reduced 90%)
Ice - Weak (No knockdown, takes 110% more damage)
Elec - Strong (Reduced 90%)
Wind - Strong (Reduced 90%)
Light - Null
Dark - Null
Almi -Strong (Reduced 90%)

Final boss of dungeon Shadow Naoto Floor 9
For this fight try to be around level 53-55

Phys -
Fire - Resist
Ice -
Elec - (No knockdown, takes 110% more damage)
Wind -
Light - Null
Dark - Null
Almi -


Optional boss for dungeon Extreme Vessel Floor 9
Try to be around 55-56.

Phys - Strong (Reduced 75%)
Fire - Weak (No knockdown, takes 125% more damage)
Ice - Weak (No knockdown, takes 125% more damage)
Elec - Weak (No knockdown, takes 125% more damage)
Wind - Weak (No knockdown, takes 75% more damage)
Light - Null
Dark - Null
Almi -Strong (Reduced 75%)

Only mini boss of dungeon World Balance Floor 7
For this boss try to be around level 56-58.

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Final boss of dungeon Kunino-sagiri Floor 10
Try to be around level 60-62

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Optional boss Lost Okina Floor 10
Try to be around level 63-64

Phys - Null
Fire -
Ice - Drain
Elec -
Wind -
Light - Null
Dark - Null
Almi -

The first mini boss of this dungeon Chaos Fuzz MM Floor 3
This fight you'll want to be around level 66-67

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

The second mini boss of this dungeon Envious Giant MM Floor 6
For this fight you'll want to be around level 68-69

Phys - Strong (Reduced 400%)
Fire - Strong
Ice - Strong
Elec - Drain
Wind - Strong
Light - Null
Dark - Null
Almi -


The final boss of this dungeon Tohru Adachi/Ameno-sagiri MI Floor 3
Try to be around level 70 to 73

Phase one Tohru Adachii
Phys - Strong
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Phase two Ameno-sagiri
Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

First mini boss of dungeon Gorgeous King Floor 4
Try to be around level 76-77

Phys - Weak
Fire - Strong
Ice - Strong
Elec - Strong
Wind - Strong
Light - Null
Dark - Null
Almi -


Second mini boss of dungeon Heaven's Giant Floor 7
Try to be around level 77-78

Boss tip: Use affinity break items
Phys - Strong
Fire - Null
Ice - Null
Elec - Null
Wind - Null
Light - Null
Dark - Null
Almi - Strong (receives 250% less damage)


Final boss of dungeon Marie Floor 10
be around level 80-85

Phase one Marie
Phys - Strong
Fire -
Ice -
Elec -
Wind -
Light - Repel
Dark - Repel
Almi -

Phase two kusumi-no-Okami
Phys - Repel
Fire - Repel
Ice - Repel
Elec - Repel
Wind - Repel
Light - Repel
Dark - Repel
Almi -

First Mini boss of dungeon Neo Minotaur Floor 3
If you did the last Dungeon then you should be a little over leveled for this one, but try to be around level 75-77.

Phys -
Fire - Weak (No knockdown, receives 450% more damage)
Ice - Weak (No knockdown, receives 450% more damage)
Elec - Weak (No knockdown, receives 450% more damage)
Wind - Weak (No knockdown, receives 450% more damage)
Light - Null
Dark - Null
Almi -

Second Mini boss of dungeon Sleeping Table Floor 6
try to be around level 77-78.

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Final boss of dungeon Izanami Floor 9
For this fight try to be around level 80-85

Phys - Strong (Receives 50% less damage)
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

Secret boss of chest The Reaper
For this fight try to be around level 73-76

Phys -
Fire -
Ice -
Elec -
Wind -
Light - Null
Dark - Null
Almi -

NG+ boss Margaret Floor 10 of Heaven (Dungeon 6)
There's a good reason only around 1% of the players on steam have beaten this boss. You should at least be around level 80; try aiming for 90 to be safe.

You're going to need this wiki page for the boss. Good luck
https://megamitensei.fandom.com/wiki/Margaret