Very fun game play, great art. and the game is pretty fair everything is just the right speed.
I think it can be improved if you made the knights appear from any of the 4 sides instead on just one, I think this would add a bit of needed randomness to the game later on, maybe you can even spawn 2 at once.
What I found to be annoying is the fact that the slime can spawn right into the player, maybe try spawning them outside the screen then let them move in (like the knight), make them unable to hit the player for a few seconds after they spawn.
Overall I would say this is the funnest game I've played from this jam so far.