perhaps give it a fixed quanta cost and instead of a count up, give it a count down.
e.g. "in 6 turns deals 100 life to opposite player"
Oh, sorry, yes, the 'X' is merely a placeholder. Not too worried about costs at the moment.
I did originally have it count down, but the more I thought about it, the more sense it made to count up instead. Gives it more of a doomy kind of feel.