Interesting but there is a lot of rules that seem broken at the final level. "Foxes doesn't cost souls" made the fox cost 2 then 1 soul, the "+1 attack when playing ants" make an unique ant I played get +2, opponent shaman doesn't look like having health bonus from card death...
Also I won and died at the same time (because of the -1 health when hitting empty slot) and the game is now blocked, can't do anything...
But balancing such game concept must be hard!