Ulamog, the Defiler

When you cast this spell, target opponent exiles the
top half of their library, rounded up.

Ward—Sacrifice two permanents.

Ulamog, the Defiler enters the battlefield 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.