The Witch King of Angmar

Flash, morgul blade, haste

This spell costs {x} less to cast, where X is the number of tapped creatures your opponents control.
This creature can only attack when all creatures that opponent controls are tapped.
At the beginning of your upkeep discard a card, if
you do: Tap target permanent an opponent controls, it doesn't untap during it's controller's next untap step.