Azaar, Nether-Deep Ruler

Azaar, Nether-Deep Ruler costs {x} less to cast,
where X is equal to the number of creatures in
all graveyards and each face-down card on the battlefield.
Flying, deathtouch, Swampwalk.
Whenever Azaar deals combat damage to a
player, you may turn face-up any number of
face-down cards you control.