Permafrost Trap

Oracle Text

If an opponent had a green creature enter the battlefield under their control this turn, you may pay U rather than pay this spell's mana cost.

Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.

Card Rulings

3/1/2010 You may target any two (or fewer) creatures. It’s okay if any of them are already tapped. If you cast Permafrost Trap for , you don’t have to target the green creature that entered the battlefield under an opponent’s control.
3/1/2010 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.
3/1/2010 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.