Fell the Mighty

Destroy target Legendary creature or
Planeswalker.
Spell mastery - If there are 3 or more instant
and/or sorcery spells in your graveyard, this spell
gains rebound (If you cast this spell from your
hand, exile it as it resolves. At the beginning of your
next upkeep, you may cast this card from exile
without paying its mana cost.)