Family Ties - S4-E17
Revealing mistake: After the New Men have captured Magneto, Wolverine, Scarlet Witch and Quicksilver, the establishing shot of the High Evolutionary's headquarters is a recycled shot of when Scarlet Witch and Quicksilver first arrived at his headquarters a few minutes earlier in the episode, played on a loop (note the lightning strikes and the High Evolutionary's pink energy field being repeated). (00:05:35 - 00:12:40)
Family Ties - S4-E17
Revealing mistake: When the High Evolutionary is asking Scarlet Witch and Quicksilver to place their arms in his DNA scanner, his mouth looks like it is jumping off his face as he is speaking. (00:06:35)
Family Ties - S4-E17
Revealing mistake: When Quicksilver is fidgeting inside his containment shell, the animators neglected to properly sync his body movement. You can see that his shoulders are not "connected" to his arms, as if his head and shoulders were separated from the rest of his body. (00:16:00)