When Guyver first appears, his blade-like top on his forehead pops up. Every other scene, the blade is still attached to his head.
As the Guyver is about to rip the arm off a Zoanoid, the view jumps to three other Zoanoids standing together reacting to it, one of them being Striker who was moments previously thrown to the other end of the scene by the Guyver.
The Guyver bends down the barrel of a revolver held by one of the thugs. In order to do this, the thug would have to be strong enough to bend it himself..
Within the last few minutes of the movie, Sean removes his Guyver armor, revealing he has no clothes on. This being due to his having regenerated a new body. But when he gets up and walks away he is wearing tennis shoes.
The Guyver's extended elbow blades wiggle and bend like rubber as he twists and turns in fight scenes.
A scene where the Guyver dismembers a Zoanoid was cut to get a PG-13 rating, revealed by a scene substituted for it: a reaction shot of three Zoanoids who were not standing together moments before or after.