There's a lot to love about this game. The graphics are on-point, the motion feels good and hitting enemies feels fantastic. Music was great too, though it could have used a different track for the bosses.
I honestly don't think hitting down to pick up items is a necessary feature. There's never really a reason you wouldn't want to pick the items up I think, so it might as well just be contact.
Slippery corners makes jumping on single-block platforms far more frustrating than it has any right being.
The whip is... inconsistent. When it's on point it feels outright amazing but when it randomly gets stuck on geometry it feels terrible. I know you included a "get unstuck" button but honestly the way the whip interacts with physics would probably need some careful thought if this project were to go further imo.
Areas not resetting when you go through a warp is pretty annoying as it can lead to you taking unavoidable damage if an enemy is camping the exit. You can also hit enemies through the screen though, which somewhat equalizes things.
The game would occasionally respawn me above spike pits, causing me to lose half my health before i got to do anything.
The length of time you're stunned for on taking damage felt a little too long to me... Due to how long it was I felt it'd end up getting me locked into taking additional damage.
I only got to fight 3 of the bosses (was there a 4th?), the chicken, the bat and the... crab.. thing. Only the bat really felt any good to fight in my opinion, the other two just felt too simplistic.
I know I've raised a number of things I didn't think felt great, but given how short a time this was developed in it's still an impressive effort. Well done!