I don't play MTG but I think if I were to design a card for it based on myself it'd have an ability that's along the lines of:
Once per round, prevent an opponent from casting a spell. When this ability is used, [Entropy] restores 1 health per mana the spell cost, up to its maximum. The spell and the mana it would have cost are discarded.
not sure what the health or damage would be though
