Whenever Karn blocks or becomes blocked, it gets -4/+4 until end of turn.
: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn.
If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.
Vigilance
Threshold — As long as there are seven or more cards in your graveyard, this creature has "When this creature dies, you may pay . If you do, return this card to the battlefield under your control."