25 Feb 2015
The ability stopping the creature from untapping will continue to apply to it even if the creature changes controllers.
25 Feb 2015
Icefall Regent’s last ability affects all spells cast by your opponents that target it, including Aura spells and spells with multiple targets. It doesn’t affect abilities.
25 Feb 2015
If another player gains control of Icefall Regent, the creature will no longer be affected by the ability stopping it from untapping, even if you later regain control of Icefall Regent.
25 Feb 2015
Icefall Regent’s triggered ability can target any creature controlled by an opponent, including one that is already tapped. In that case, the creature stays tapped and won’t untap during its controller’s untap step.