The Darkest Hour: Part Two - S4-E2
Revealing mistake: At the very beginning of the episode, as the knights are about to send Merlin to Camelot with Lancelot, the knights walk towards the camera. As they do, there's a patch of green screen the special effects department must have forgotten to remove between Sir Elyan and Sir Percival. (00:02:10)
The Cavern - S1-E10
Revealing mistake: When Jonathan and Nicky are running out of The Cavern during the rockfall a cabinet is knocked over by the vibration, but you can see that it is pushed over by someone with a stick.
Firefly, Light My Fire - S1-E1
Revealing mistake: Courage winces and reacts before the stereo-zapper is fired.
Revealing mistake: During Kendrix's morphing sequence you can see that the editor did a poor job photoshopping the Ranger helmet and you can still see the white edges of whatever photo they used. It should be tight to the Ranger's helmet and costume like the rest.
Revealing mistake: Angelica and the other children are about to crash through the door to attack Lyra and Will. As Lyra runs past a cabinet, a lamp sitting on top is knocked over and crashes to the floor. Dafne Keene, who plays Lyra, reached over and very obviously pushed the lamp to the floor.
Revealing mistake: During the final battle there is a dual between Julius Caesar and Gannicus. At one point Gannicus spins Ceasar around and he is shown to wear modern day underwear.
Lightspeed - S5-E8
Revealing mistake: When the HIVE Five exit the museum and are intercepted by Kid Flash, Mammoth loses both his pants and the artifacts he has before KF whizzes past him. It's best seen in slow motion; at normal speed this mistake is hard to catch.
Revealing mistake: Janet is holding a coke in her hand that she is supposed to be conjuring up but is already holding it.
Revealing mistake: When everyone is supposed to be frozen, the neighbor girl standing behind the car can be seen moving her hand onto the car. This happens as Monica says "I'm not afraid of you, Wanda." (00:24:25)