Instill Energy

Oracle Text

Enchant creature

Enchanted creature can attack as though it had haste.

0: Untap enchanted creature. Activate this ability only during your turn and only once each turn.

Card Rulings

10/4/2004 If attached to an opponent’s creature, you can untap their creature during your turn.
10/4/2004 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.
8/1/2005 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.