Dead Cells

Kinda a no-brainer, but just in case, you need to beat the game with two boss cells active. You can use the assist mode options to knock enemy damage and health down to 20%. You can also use infinite lives, and restart at a checkpoint. You can use an Aspect as well (like boosted fire or ice damage) but then you will not receive your 3rd boss cell, so its advised not to use an Aspect in this run.