Karn, Silver Golem - 298 R USG

Whenever Karn blocks or becomes blocked, it gets -4/+4 until end of turn.
{1}: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn.

rare
Legendary Artifact Creature — Golem
From the Magic: The Gathering set Urza's Saga.