You should use counters to track how many times it's been used. I also think because the way draw is defined you might want to say something like "If you would draw a card, you may exile the top card of your library instead. If you do, gain life equal to its mana value and put a fast counter on ~. Then if there are 4 or more fast counters on ~, exile it."
Edit: You also probably want it to say "you may play cards exiled..." rather than "cast." Otherwise it would feel really bad to hit lands off of this.
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u/Handyandyman50 21h ago edited 21h ago
You should use counters to track how many times it's been used. I also think because the way draw is defined you might want to say something like "If you would draw a card, you may exile the top card of your library instead. If you do, gain life equal to its mana value and put a fast counter on ~. Then if there are 4 or more fast counters on ~, exile it."
Edit: You also probably want it to say "you may play cards exiled..." rather than "cast." Otherwise it would feel really bad to hit lands off of this.