I got stuck at the bottom of the level as a paladin... I couldn't jump onto the princesses crate because there was another block diagonally above hers...
It'd be nice to not have the reset button the spacebar -- I keep accidentally hitting it. Also, the chances of keyboard cat hitting it are higher as well!
A few glicthes --
Assassin health bar gets screwy sometimes.
When rage is fully upgraded all it does is freeze my computer for that duration.
Other than that -- more upgrades, and make it harder. It's very easy.
I hated biology -- it was boring. But this, this in fun and I think I've already learned more than my entire year of Bio. Keep making educational games, you've got a knack for it! :D