Revealing mistake: When the Grand Ville turns onto the street where the children are playing, it clips a parked car as it makes the turn. This is the same car that later gets its driver's door ripped off by the Grand Ville just before the police give chase. It was repainted red for the second scene, but note the same dent in the right fender as before.
Revealing mistake: Right at the end when John is dying look at the texture of his blood. It is way too thin, almost like coloured water.
Revealing mistake: Near the beginning, Megalon steps out from behind a mountain. It's obvious the "mountain" is a cardboard cutout.