Just some random idea I had.

Maybe there could be a colluseum where you fight wave after wave of various baddies, and be rewarded gralats based on how many waves (possibly also depending on the difficulty of the wave and overall difficulty the player selects) the player completed before dying. Might possibly need the player's hearts to be set to a certain amount (probably more than three) and it'll definitely have to refill the player's hearts after each wave.  

Interesting idea. There isn't really enough variety in baddies or their difficulty though, so it wouldn't be very exciting if it were implemented with the current baddies.  

You can always give some baddies a health buff or sword buff pertaining to their color armor I suppose. Or maybe throw in those spider crab freaks that shoot rocks and bats and slimes while you're at it.  

Baddies are stupidly bugged, anything with them fighting in hordes will be stupid. They'll do more damage to themselves than you will to them.