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'.
Continuity mistake: In episode 17 of season 4, "Tequila Mockingbird," Max is going to pour tequila in Valdez's glass. The camera closes up to show Max picking up a bottle with a candle on it. The candle falls into the glass. When the camera angle changes to show Valdez and Max, the candle is gone.