Creature - Giant Warrior 3/3, 4RR (6) Trample Tap an untapped red creature you control other than Impelled Giant: Impelled Giant gets +X/+0 until end of turn, where X is the power of the creature tapped this way.
Illus. Mark Zug
Because there is no {Tap} symbol in the cost, you can tap creatures that were not in you control since the beginning of your most recent turn. [Eventide FAQ 2008/07/08]
The power of the creature is checked only on resolution. [Eventide FAQ 2008/07/08]