2010-03-01 : If a targeted creature is untapped at the time its controller’s next untap step begins, the second part of the ability has no effect on it.

2010-03-01 : If an affected creature changes controllers before its previous controller’s next untap step, this ability will prevent it from untapping during its new controller’s next untap step.

2010-03-01 : You may target any two (or fewer) creatures. It’s okay if any of them are already tapped. If you cast Permafrost Trap for {U}, you don’t have to target the green creature that entered the battlefield under an opponent’s control.