Mirotalac, the Twister

At the beginning of each opponent's upkeep, for
each creature that player controls with neither
power nor toughness equal to its converted mana
cost, you gain control of that creature unless that player pays life equal to its converted mana cost.
When Mirotalac, the Spinner leaves the battlefield, sacrifice all creatures that you control
but don't own.
Existence is imperfect. The void is eternal.