Very fun prototype! With sound effects and more visual feedback this could be a blast.
The gameplay feels very intuitive, as soon as you find the burn pile and see the mana. And the art is very nice.
I'd like to see the ability to move a card in play to a free slot, maybe for 1 mana. Maybe just for the player.
The game seems to bug out and crash if you continue playing after being booted back to the menu after beating 3 enemies. It was offering me a new card every turn and then threw a Javascript error.