Opponents' artifacts can't activate. Put 5 loyalty (use counters) on Karn. Opponents can attack Karn as though he were you. Any damage he suffers depletes that much loyalty. If Karn has no loyalty, he abandons you. During your turn, you may add 1 loyalty to turn target non-creature artifact into an artifact creature with both power and toughness equal to its casting cost until your next turn; or you may spend 2 loyalty to put an artifact card from outside the game into your hand.