Ulamog, the Defiler (Borderless) (383) [Modern Horizons 3]

When you cast this spell, target opponent exiles the top half of their library, rounded up. Ward—Sacrifice two permanents. Ulamog enters with a number of +1/+1 counters on it equal to the greatest mana value among cards in exile. Ulamog has annihilator X, where X is the number of +1/+1 counters on it.