Ava, Sibyl of the Mirage

Whenever Ava attacks, exile the top three
cards of your library. You may cast one of
them. Put cards not cast into your graveyard.
{x}{w}{r}, {t}: Exile creature cards from your graveyard with total converted mana cost X
or less. Create tokens that are copies of them.
They gain haste. Exile them at end of turn.