Boqias, the Mutated

Skulk, Changeling
Whenever Boqias the Mutated deals combat
damage to a player, choose a creature type. Look
at the top X cards of that player's library, where
X is the number of creatures of the chosen type
you control. You may choose one of those cards
and exile it face down. You may look at and cast
that card for as long as it remains exiled.