Deliberate mistake: There is a shot of Alexis getting blasted with electricity when Etoile Cyber is attacked by Sparkman. This same shot is reused later in the episode when she attacked directly by Elemental Hero Thunder Giant, as the electricity and Alexis' position in the shot is the same. (00:12:20 - 00:18:36)
Deliberate mistake: Identical twins Beverly and Elliot have the exact same beauty mark on their faces, roughly on the smile line directly across from the right nostril. Identical twins don't share features like that.
Night of the Sentinels: Part 1 - S1-E1
Deliberate mistake: When the Sentinel is first walking through the mall, its footsteps are so heavy that it shakes the building. When it is shown walking past the shop Gambit is in, there is no shaking of the building, presumably done so Gambit wouldn't notice it. (00:04:08)
Deliberate mistake: Whenever Dexter injects somebody with M99, they are immediately rendered unconscious. In reality, this would take several minutes.