The Origin of the Fantastic Four: Part 1 - S1-E1
Other mistake: When Puppet Master is making a clay figurine of Thing, the mold he uses doesn't have a Thing-shaped interior with which to make a detailed figurine. The figurine should have just looked like an undefined human-shaped figure. (00:15:20)
Sins of the Fathers Chapter 8: The Ultimate Slayer - S3-E8
Other mistake: When Kingpin is berating Smythe over his failure to kill Spider-Man, the camera footage Kingpin is showing of Spider-Man is merely clips from previous episodes.
Other mistake: When Iron Man tells Mandarin that he's been waiting to meet him face to face, they are standing only a few yards apart. Mandarin retorts by saying "Then face this, Iron Man," while firing an energy blast from one of his rings at him. The shot changes and Iron Man is hit by the blast. With how fast the blast was shown traveling and the short distance between the two, Iron Man would have been hit by the blast before Mandarin could have finished saying his comeback line. (00:14:38)