Crush of Coffins

When Crush of Coffins enters the battlefield,
exile target creature an opponent controls and
entomb X, where X is the exiled creature's
converted mana cost. (Exile the top X cards of
your library face down. A player may look at any
entombed cards they own at any time.)
When Crush of Coffins leaves the battlefield,
return the exiled creature to the battlefield and
return target entombed card to its owner's hand.