Factual error: When the bully has been shocked and his heart stops, Powder zaps him back to life. Okay, fine, but as a former ER nurse I noticed some flaws. 1) You can not get a person's heart beating by defibrillating if he's flatlined. You need some sort of activity in the heart first. If Powder had started with some CPR, possibly. 2) Defibrillating someone in a puddle of water? Bad move, unless you assume that Powder's immune to his own shocks. And 3) when defibrillating you hold one paddle on the sternum (middle of the chest) and one on the left side of the ribcage, thus allowing the electricity to go between the paddles and through the heart. The way Powder held his hands really wouldn't have worked.
Continuity mistake: Near the end, when Powder and the girl are sitting at the picnic table, the girl's father runs up and grabs Powder. The girl stands up and steps over the picnic table bench. The scene cuts to a closeup of Powder, then back to a wide scene where the girls is standing up and stepping over the bench again.
Continuity mistake: When Jeremy is pulled to a standing position from the bench, notice Powder's jacket collar after her father grabs and then releases him. At first it's up, then it's down and then it's up again.
Continuity mistake: In the very first shot in the movie an ambulance is driving to the hospital with one of the left headlights out and one of the red lights out. In the next shot, as the ambulance pulls up to the hospital, the broken headlight switches to the right side, both red lights are now working, and now the name placards that say "GRAHAM" are not lit up anymore.