Karn, Silver Golem is a mythic Legendary Artifact Creature — Golem card from From the Vault: Relics (V10), collector number 6. Current market price: — (foil $16.95), TCGplayer market prices via Scryfall.
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.