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)
Neogenic Nightmare Chapter 8: Duel of the Hunters - S2-E8
Other mistake: After falling down the cliff and getting blasted back by his van's explosion, the Punisher shows no signs of injury. This kind of fall combined with explosion should have killed him, or at least injure him very severely, as he is a normal human without any superpowers.
Other mistake: When Firebrand is in the back of the police car, his handcuffs are the same yellow-orange color as most of his costume, and half of the front passenger seat is missing. (00:19:19)