Great game! Fun idea, I really like it. The animations are smooth and I like the particle effects. Music was a bit loud though so maybe a menu slider or just tune the sound down by default.
Some things I noticed:
You don't seem to check if the player is grounded when jumping. This leads to some behavior where the player can jump off of walls or even the bottom of platforms. While I don't think continuously smashing your head against the bottom of a platform to levitate is something you want in your game, jumping off walls when timed well actually leads to a boost-jump effect, where the player goes flying into the air, which is really fun to do. This also can tie into your character as a ninja, so that might be something you look into making a proper mechanic.
There is a part of the game where zombies are blocked behind a crate, I found that shooting a knife at the box makes the box jump and the knife shoots out the bottom on the other side. I thought this was really fun! If this is intentional, maybe teaching the player through natural gameplay, by caging a zombie behind a box so the only way to reach is is by throwing a knife at the box, could be a cool idea.
The control scheme with R as a fire key is hard to play, as I am using my left hand already for wasd and space. Perhaps consider a key on the right side of the keyboard for the player to use their right hand, or map shooting to a mouse key.
Bugs:
If you land on a ladder while falling, it makes climbing up the ladder extremely slow.
Dying on certain levels makes the game crash. Not sure why.
Overall I really liked playing this game, a great submission! Congrats on completing the jam.