Activated abilities of artifacts your opponents control can't be activated.
+1: Until your next turn, up to one target noncreature artifact becomes an artifact creature with power and toughness each equal to its converted mana cost.
−2: You may choose an artifact card you own from outside the game or in exile, reveal that card, and put it into your hand.

MAGIC THE GATHERING - KARN, THE GREAT CREATOR - WAR OF THE SPARK is categorised COLLECTIBLE CARD GAMES / MAGIC: THE GATHERING and sold by l'Imaginaire, a store and specialised website.