Instill Energy
Enchantment — Aura
Enchant creature
Enchanted creature can attack as though it had haste.
: Untap enchanted creature. Activate only during your turn and only once each turn.
Dameon Willich
Masters Edition IV (ME4)
• #157Rulings
Any Auras (or other effects) which are on the creature that would cause it to not be untapped (or have a cost to be untapped) during untap step do not in any way hinder or imply a cost to use this card's ability to untap once during the turn.
(wotc • 2005-08-01)
Instill Energy's untap ability will not untap the creature until it resolves. This means other spells and abilities can be used before it actually becomes untapped.
(wotc • 2004-10-04)
If attached to an opponent's creature, you can untap their creature during your turn.
(wotc • 2004-10-04)
Rulings
Any Auras (or other effects) which are on the creature that would cause it to not be untapped (or have a cost to be untapped) during untap step do not in any way hinder or imply a cost to use this card's ability to untap once during the turn.
(wotc • 2005-08-01)
Instill Energy's untap ability will not untap the creature until it resolves. This means other spells and abilities can be used before it actually becomes untapped.
(wotc • 2004-10-04)
If attached to an opponent's creature, you can untap their creature during your turn.
(wotc • 2004-10-04)