Headbutt's issue is that so many of Ironclad's best cards are Powers or Exhaust cards, so you can't put them back on top of your deck after playing them. Further, putting a /different/ card on top of your deck can make it take longer to find them. If I take a Headbutt, it's probably because I got a very good non-Exhaust Uncommon early, like Flame Barrier or Battle Trance, and don't have enough damage in my deck yet.
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