The triggered ability can target any creature, including one that is already tapped. In that case, the creature stays tapped and won't untap during its controller's untap step.
2020-11-10
If another player gains control of Merchant Raiders, the creature will no longer be affected by the ability stopping it from untapping, even if you later regain control of Merchant Raiders.
2020-11-10
The ability stopping the creature from untapping will continue to apply to it even if the creature changes controllers.
Whenever this creature or another Pirate you control enters, tap up to one target creature. That creature doesn't untap during its controller's untap step for as long as you control this creature.
