Hovering Troodons

Hovering Troodons enters the battlefield under the control of an opponent of your choice.
Whenever you untap a nonland permanent, tap target untapped permanent you control.
Sacrifice a creature; Target player gains control of this enchantment.
"First you see the glow in the night. Then you hear the scream. By the time you can see the claws and teeth, it is far too late."