Karn, the Great Creator (Secret Lair Drop 253) - Rare Magic: The Gathering Card

Activated abilities of artifacts your opponents control can't be activated.
: Until your next turn, up to one target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value.
: You may reveal an artifact card you own from outside the game or choose a face-up artifact card you own in exile. Put that card into your hand.