Karn, the Great Creator

2019-05-03 A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.
2019-05-03 Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text, such as equip. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by Karn.
2019-05-03 If a permanent has {X} in its mana cost, X is considered to be 0.
2019-05-03 In a casual game, a card you choose from outside the game comes from your personal collection. In a tournament event, a card you choose from outside the game must come from your sideboard. You may look at your sideboard at any time.
2019-05-03 Karn's first ability affects only artifacts on the battlefield. Activated abilities that work in other zones can still be activated.
2019-05-03 Karn's last ability can't get a face-down card in exile, even if you know it's an artifact card.

Card is in preconstructed decks:

mtg.wtf