Hannah, Delver of Secrets

Whenever Hannah, Delver of Secrets enters the battlefield, each opponent puts the top X cards of his or her library into his or her graveyard.
Whenever Hannah, Delver of Secrets attacks, you may return any creature card from any graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step.
{t}: Put a card an opponent owns in exile into their graveyard. Untap Hannah.