Urza, Unhinged Artificer

-1: Create a legendary artifact token named Mightstone. It has indestructible and "attacking creatures you control gain +1/+1 until end of turn."
-1: Create a legendary artifact token named Weakstone. It has indestructible and "attacking creatures you don't control get -1/-1 until end of turn."
0: Sacrifice Mightstone and Weakstone to deal 20 damage to each creature, planeswalker, and player. This damage cannot be prevented.