Diablo, The Prime Evil

Diablo costs {x} less to cast, where {x} is 7 minus the number of cards in your hand.

Whenever a non-permanent card is put into your graveyard from anywhere other than the battlefield, it enters with a pact counter on it.

While you have no cards in hand, you may cast spells from your graveyard with pact counters on them by paying 3 life in addition to its other costs.

Pay 3 life, Discard a card: Each opponent discards
a card or loses 3 life. Surveil.