Zyzahl, Master of Riddles

Flying
Whenever a sphinx enters the battlefield or attacks
target player speculates. (Exile the top card of their
library face down. That player guesses if that card has
converted mana cost higher than four. If that player chooses correctly, they put that card into their hand
and create a treasure token.)
You may cast cards exiled with speculate as long
as they remain in exile and pay {u} for all colored
costs.