Fun game, I've played a lot over the last two weeks and here are my thoughts/feedback:
It's always a good idea to carry a Berserk card to the end. Boss fights can turn badly really quickly and a Berserk card could make the difference between you winning or losing.
The Vampire's bite doesn't affect the undead, It's not always obvious which enemy is undead though. I think that a description should be added that says if an enemy is undead or not.
I had a bug where I beat the final boss (Evil Eye) but then the game didn't end. It kept going forever. This was on Firefox (Windows).