Tomorrow is Yesterday - S1-E20
Factual error: Towards the end of the show the Enterprise is leaving Earth orbit and heading towards the sun. We see the Earth diminish and the moon appear looking exactly as it does from Earth. From this angle we should be seeing the "dark side" of the moon, which looks completely different. (00:40:50)
Factual error: The tanks, half-tracks and self-propelled guns are modern American vehicles painted in a a bright yellow color rather than a muted desert sand color. The only vehicles which actually did see action in North Africa in WW2 would have been the M-7 Priest Gun Motor Carriage and the M3 half-tracks being used by the Germans in "The Rat Patrol."
Factual error: When Ulysses opens his mouth while speaking, modern dental fillings are in his teeth.
The Clock King Gets Crowned (2) - S2-E12
Factual error: Trapped in the overturned hourglass, Batman and Robin lie flat and begin furiously digging in the sand, making the hourglass roll out the door. But to cause such rapid movement, they'd need to be applying their weight against one of the glass sides (like a hamster in a ball). Just digging in the sand wouldn't get them anywhere, at least not that quickly. (00:04:15)
The Jewels of Topango Affair - S1-E14
Factual error: Mark plays his electric guitar for the tribal chief, and the amplifier works just fine, despite the fact that it isn't plugged into any power source. (00:17:00)
Factual error: 1968: The basement's brick wall crumbles to reveal Trask's skeleton hanging in the alcove. Only it shouldn't be. Bodies do not remain assembled once the flesh and sinew are gone. Trask's remains ought to be a large pile of bones on the floor.
The Legacy - S1-E15
Factual error: For supposedly being Hitler's heirs, the three conspirators are pretty lousy Nazis. None of them notices that on their copy of their idol's book, Mein Kampf, Der Fuhrer's name is prominently misspelled "Adolph" instead of "Adolf." (00:13:00)