Ahrmira, Rogues Codex

Eminence - As long as Ahrmira, Rogues Codex is in the command zone or on the battlefield, rogue creature spells you controle have theft. (Whenever this creature deals damage to an opponent, look at the top X cards of his library, where X is damage dealt this way. Exile one of them face down, then put the rest on the bottom of that library in a random order. You may look at and cast that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell.)