Other mistake: For secret agents, Sydney and Dixon are not very dedicated to secret identities. At several points they refer to each other by their real names in front of other people while they are under aliases. Examples include The Confession party and The Coup Las Vegas scenes.
The Breach - S2-E21
Other mistake: As Archer walks into the sickbay, while the camera pans, you can see a bottle of Crystal Geyser water. I noticed the bottle right away but had to pause it to see the brand. (00:39:00 - 00:40:00)
Other mistake: In the party/orgy scene where Aetius is showing off Rome to Attila, one can see a woman with her back to us reveal herself to a man and woman. Despite her veil, one can see her thong underwear. This type of underwear is a 20th century innovation.
Replacements - S1-E4
Other mistake: When Heffron is taking his throw at darts, he states that he needs a "double seven". When he takes the throw, the dart goes into the treble eight (an earlier close-up confirms that the board has the standard Gamlin configuration), yet, from the reaction he gets, he's made the throw he was going for. (00:04:40)
Injustice For All (2) - S1-E19
Other mistake: Unless he escaped prison, it makes no sense for Copperhead to be in the police van with the other Secret Society members. You can see him sitting there across from Solomon Grundy and The Shade.
Other mistake: Two Tiffs can be seen for a few seconds when King Dedede and Escargoon drive in.
Other mistake: In this episode, Eric tries to destroy a mutant, apparently unaware that Rangers don't destroy mutants but freeze them. Yet in Quantum Quest and Clash for Control, he froze a mutant.