Ashiok, Dream Reaper

+2: Tap target permanent. It does not untap during its controller's next untap phase. If it is a creature, its creature type is now Nightmare.
-4: Gain control of target tapped creature or target Nightmare creature. It gains skulk for as long as you control it.
-9: Target player gets an emblem with "You do not not untap more than one permanent you control during your untap step."