Continuity mistake: Episode 16, season 4, "The Day They Raided the Knights." In Max's apartment, Max sneaks up behind 99 to give her a kiss. She punches him in the jaw and he falls back against the wall to the right of the doorknob. The scene changes to a close up of Max and he is sitting on the floor to the left of the doorknob.
Character mistake: Season 2, Episode 27 'Pussycat Galore' : Maxwell translates his famous line "And loving it' into the German 'Und damit gefreut'. Agent 99 who claims to speak German fluently confirms it. This translation is both far away from the meaning and doesn't make any sense at all. The right translation is 'Und liebe es'. (00:09:50)
Visible crew/equipment: When Max and 99 have reached the mansion, they both get out of the car to look in the trunk. As they start walking, some lightning occurs. If you look up at the top, you can see where the fake sky ends and the visible back of the stage begins.
Plot hole: In this episode, the villain makes a phone call to KAOS headquarters when he's captured demanding that they kill Max to stop him testifying in court against him. Later, several say that Max is the only witness to the villain's crimes, but the Chief and 99 were in the room when the villain made the call, so they could have been witnesses to "conspiracy to commit murder."