Character mistake: When Matt is talking to his priest Father Lantom, he says "it was a nice sermon" instead of "it was a nice homily." In the Catholic church "homily" is the correct word; sermons are Protestant. (00:11:30)
Continuity mistake: A henchman places a briefcase up-side down on a bench, opens the locks and starts to open the briefcase with the locks above the lid latches which are flipped open toward the floor. Instantly the briefcase is right-side up with the locks down and the lid latches up. (00:26:11)
Continuity mistake: As they are fleeing the alien base, Supergirl and the others run towards the portal, Winn activates it and jumps through. In a following shot (after a 'friendly' alien helps them), he is standing behind Supergirl again. (00:32:00 - 00:32:35)
Other mistake: John is promoted to Oberst Gruppenfeuhrer and assumes the uniform of such. He is soon after promoted to interim Reich Marshal. And then he is subsequently fully promoted to Reich Marshal. But he continues to wear the rank insignia of an Oberst Gruppenfeuhrer.
Factual error: There is a periodic table shown in the background of the lab, showing an accurate periodic table as of now. During 1945, at least 21 elements had not been discovered. (00:17:40)
Here There Be Dragons - S2-E11
Visible crew/equipment: When Prax leads the group to where Dr. Strickland took Mei, just as they reach the door the two green and yellow T-marks are visible on the floor. (00:02:30)
The Two Deaths of Jamie B. - S2-E4
Revealing mistake: When Naomi shows Kirsten the money, you can tell it's fake. Not only are the serial numbers all the same, you can read "this note is not real it is to be used for motion pictures."
Us vs. Them - S2-E2
Factual error: We see Liam's driver's license. It says he's from Rhode Island, but the license looks nothing like RI's. It's issued by the State Motor Vehicle Commission, but RI does not have an MVC (only New Jersey does). And the expiration date is always the same as the holder's birthday, but here we see it's 2 days after his birthday.
Continuity mistake: The quantity of super-steroid in Fukegao (the mad scientist) 's test tube changes continuously between shots. (00:11:00)
Factual error: As Ren enters Renautas and meets Emily, the word "Welcome" keeps scrolling in various languages on the screens in the background. Although hardly seen, the Hebrew is wrong, as it is reversed (text from left-to-right, as opposed to right-to-left).