Incredible work here! It's brimming with the gameboy vibe and it's so well executed. The art and musics are delightful! I think it's very impressive that this got made within the jam's period.
My only tiny issue is with how much damage the enemies deal, mostly that bat enemy that always got me. And about the bump mechanic I think it's very cool and quite unique but it needs some minor tweaks, maybe giving iframes to the player after getting hit or getting more feedback if you dealt damage to a enemy or not.
But overall I've really enjoyed your game, congrats!