Some ideas I had (check description)

Lore thingy where you can go and be that enemy from the past to learn their lore I’ve already posted this one

shadow nyan ends the battle early and after all the lights break having you to fix them (shadow nyan will roam and chase but as a NPC if catches you shadow nyan will throw you to the ground and the game goes back to where you are fighting shadow nyan)

You can go to a cage with a enemy in it to fight them again (and you can make them harder and you have to beat the enemy before them appearing in a cage)

roaming mode this mode will activate in some areas (via the shadow nyan area) making you have to hide or defend yourself from the enemy by setting traps

That’s all :)