1 is okay, but doesn't solve the cheap ignite problem.
2 isn't a good answer because like QuantumT said, you need another element anyway and a rainbow could still abuse the card
3 or 4 are probably the best, but then it becomes rather useless unless you get the buff card
I still like the idea, and if it was any element other than fire, it probably wouldn't be a problem. It's just cremation that really makes it difficult to balance.