The slowdown effect when you lose is awesome. This game has better polish than a lot of my 48 hour game jams!!
One thing I struggled with was the special powers. It seems like when an enemy dies, there's some kind of special power that happens, like the lightning or the acid. But I still can't tell if the specific power is chosen from the card that killed them or if each chess piece does something different when they die. Some more instruction on that would be nice.
I can't think of much more to say - excellent game!