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Karn, Silver Golem

Whenever Karn, Silver Golem 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.

Vintage Masters

Whenever Karn, Silver Golem 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 converted mana cost until end of turn.

Commander's Arsenal Oversized

From the Vault: Relics

World Championship Decks 1999

Arena League 1999

Urza's Saga

Whenever Karn, Silver Golem blocks or becomes blocked, it gets -4/+4 until end of turn.
o1: Target noncreature artifact is an artifact creature with power and toughness each equal to its casting cost until end of turn. (That artifact retains its abilities.)