Preacher

You may choose not to untap this creature during your untap step.
{T}: For as long as this creature remains tapped, gain control of target creature of an opponent's choice they control.

Magic Online Promos

Masters Edition

You may choose not to untap Preacher during your untap step.
{T}: Gain control of target creature of an opponent's choice that he or she controls as long as Preacher remains tapped.

The Dark

oc
T: Gain control of one of opponent's creatures. Opponent chooses which target creature you control. If Preacher becomes untapped, you lose control of this creature; you may choose not to untap Preacher as normal during your untap phase. You also lose control of the creature if Preacher leaves play or at end of game.

The target of the ability is a creature the chosen opponent controls. As the ability resolves, if the target isn’t a creature controlled by the chosen opponent, the ability won’t resolve. If the ability’s target is changed somehow, the new target must be a creature controlled by the chosen opponent.

When you activate the ability, you choose an opponent, then that opponent chooses the target.

Whether Preacher is tapped is checked continually, starting when the ability is activated. If, before the ability resolves, there’s any point at which Preacher is untapped, the ability has no effect — even if Preacher is tapped again by the time the ability resolves.