The Mask of Doom: Part 3 - S1-E10
Other mistake: After Thing breaks the chains he, Reed and Johnny were bound to, Johnny's cufflinks simply slip off his hands. Breaking chains wouldn't magically cause the cufflinks to now be able to slip off a person's hands. And if Johnny was able to slip them off anyway, he wouldn't have needed to wait for Thing to break the chains to do so. (00:14:19)
The Mask of Doom: Part 3 - S1-E10
Revealing mistake: When the Persians are rowing the boat, four of them have the same face. (00:13:23)
The Mask of Doom: Part 1 - S1-E8
Other mistake: When Reed, Johnny and Thing come upon the hall or mirrors, Reed and Johnny do not cast any reflections until Reed notices that the mirrors are about to attack them with lasers. (00:19:16)
Superskrull - S1-E7
Audio problem: When Johnny is saying "Ben sold our rights to MTV. We're going to be rock stars," his mouth movement is not in sync with the dialogue. (00:07:16)
Superskrull - S1-E7
Continuity mistake: When the noxious slime slug is approaching Super Skrull, it spews its slime at his feet. When the shot changes, the slime is gone. (00:05:00)
The Silver Surfer & the Coming of Galactus: Part 1 - S1-E5
Other mistake: When Uatu is attempting to shield Earth from the Silver Surfer's view, the brown car driving down the street is somehow smaller than the pedestrians to its right. (00:11:58)
Now Comes the Sub-Mariner - S1-E3
Other mistake: When Johnny is playing the guitar by the fire, you can hear different chords playing, but he is neither strumming or moving the fingers of his fret hand to form different chord shapes. (00:06:15)
Now Comes the Sub-Mariner - S1-E3
Other mistake: When the mutated octopus begins crawling out of the tank, the camera pans to the right, and you can see the animators drew parts of Reed and Johnny's legs and feet to resemble Thing, making Thing resemble a giant ball of rocks. (00:02:30)
The Origin of the Fantastic Four: Part 2 - S1-E2
Other mistake: When Johnny is pursuing the Puppet Master's helicopter, Puppet Master rotates the helicopter 90° in an evasive maneuver. You can see Puppet Master and Sue were not wearing seatbelts, so they both should have fallen out. (00:11:41)
The Origin of the Fantastic Four: Part 2 - S1-E2
Plot hole: When Thing breaks down Puppet Master's secret door, the heroes see that he is already in a helicopter flying away. Since the secret door lead directly to the outside of the building, and they were a couple floors up, there would have been nowhere for a helicopter to be waiting for Puppet Master to climb into. (00:11:28)
The Origin of the Fantastic Four: Part 2 - S1-E2
Factual error: When Puppet Master takes a picture of the prison warden on TV with his Polaroid camera, the picture emerges instantly developed. Those types of pictures never develop instantly. (00:03:32)
The Origin of the Fantastic Four: Part 1 - S1-E1
Factual error: After the group has crash-landed back on Earth and Sue is saying "We're all alive," the moon behind everyone is far too large. (00:06:34)
The Origin of the Fantastic Four: Part 1 - S1-E1
Continuity mistake: When the shuttle crash-lands back on Earth, it is twilight. When the group exits the shuttle, it is suddenly dark outside.
Suggested correction: There's no way of knowing how long they were in the shuttle after it crashed, what happened to them, or what they might have been doing. It seems it's just meant to show a passage of time.