Stupidity: When Dr Loomis and Sheriff Bracket are chasing who they think to be Michael Myers, you can tell that it isn't him. Michael Myers is supposed to be 6'2 - Ben Tramer is maybe 5'4. If Michael was shot 6 times there would be blood on his overalls. And the mask that the kid is wearing has blonde hair, whereas the mask Michael wears is brown.
Stupidity: When the shuttle arrives with the assassins, O'Niel is shown loading a shotgun, then he carries that gun when he runs to his office. When he leaves his office again to confront the assassins he grabs another shotgun from the locker. Why didn't he just grab the gun he walked in with?