Self-regen and insane versatility. 3 cost for a maximum of 9 damage or 9 threat removal over 3 turns without using self-regen. I'm surprised this card isn't over-costed garbage like most cards seem to want to be. Auto-include in any Magik deck I run.
Great voltron. Any deck that specializes in any resource could consider using Legion. Also another option that works for Domino and discard decks but doesn't work with wilds unfortunately. Work with multi-resource cards for characters like Rocket Racoon, Bishop, and the the upcoming Jubilee.
Similar to Adam Warlock who has to discard a card from hand instead of from the top of your deck. And Hulk.