Obelisk

Haste, Menace, Shroud
As an additional cost to cast Obelisk, sacrifice 3 creatures. Obelisk enters the battlefield with X
+1/+1 counters.
{x}{u}{b}{t}, Exert Obelisk: Sacrifice 3 other
creatures: Destroy all creatures target opponent controls with converted mana cost X or less.
They can't be regenerated.