Betrothed of Fire
Sacrifice an untapped creature: Enchanted creature gets +2/+0 until end of turn.
Sacrifice enchanted creature: Creatures you control get +2/+0 until end of turn.
4/1/2008 If you control Betrothed of Fire, but it’s attached to a creature you don’t control, no one can activate the last ability. The creature’s controller can’t activate it because that player doesn’t control the Aura. You can’t activate it because you can’t pay the cost — you can’t sacrifice a creature you don’t control.