A great platformer that shows lots of potential!
The combat system coupled with the Infection/Fever modes is an idea I would love to see fully realised. I was not enjoying the Infection/Fever mode in the beginning, but after playing and dying many times, I grew to like it a lot.
In my opinion, the controls could use a small change. Up / W is un-used at the moment, maybe this could be Jump instead? Then Spacebar could be to attack. I think this would help the player a lot as the distance between Shift and O is quite confusing when you need to utilise them together so often.
The enemies also felt a little overpowered. Do they drag you closer to them when they attack?
My final feedback is the player control. This is not something that is important at all during a game jam - only if you would work more on the game (I think you should - it is a really interesting concept). The player is currently rather "floaty". As in there is a delay when starting and stopping movement before the character gets to full speed or stops. I realised you had a number of "precision platforming" areas... and these do not gel with the "floaty" feeling of the character (to me). So I would recommend either making that delay very short, or removing it all together. As a pixel art game, it's not too important that the movement is "smooth" like what is normal with other artstyles. This would make those precision areas fun and challenging. Or you could also consider removing the precision areas.
Other than this, the game is visually great, audibly stunning and very playable! Well done!