Deliberate mistake: When Johnny is watching the news footage of the Hulk battling Thing, all the footage is merely clips from that portion of the episode, including parts of the battle that were happening before the camera crews even showed up. (00:02:50 - 00:07:20)
Continuity mistake: When Sue is talking about her father going into hiding, the camera is on the right side of a photo album, showing a newspaper clipping of him being wanted for murder. When the shot changes, the contents of that page are now three different photographs. (00:07:32)
Continuity mistake: This series is in the same continuity as the other Marvel animated series that aired around the same time - X-Men, Spider-Man, Iron Man, and The Incredible Hulk - by virtue of each aforementioned show crossing over with at least one of the others. This episode, which originally aired on November 4, 1995, features a cameo appearance by She-Hulk. However, Jennifer Walter's didn't become She-Hulk until the season 1 episode of The Incredible Hulk entitled "Doomed," which originally aired on November 3, 1996. We know "Doomed" takes place after this episode, because the later episode of this series, entitled Nightmare in Green, features a plot where Dr. Doom meets Hulk for the first time after discovering that he is also Bruce Banner, and attempts to use him to destroy the Fantastic Four, and "Doomed" showcases Dr. Doom once again trying to use the Hulk to suit his own ends.
Plot hole: When Frankie tries to get Johnny to chase her out into space, he tells her he can't follow and warns her to turn back due to the thin atmosphere not being able to keep their flame powers active, and indeed her flames die out, and she begins falling back to Earth. However, several minutes later in the episode, both of them are just outside of the Earth when Terrax arrives, and again at the end after she becomes the new herald of Galactus, Johnny follows her into space well beyond Earth before his flames die out. (00:03:15 - 00:06:03)
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)
Plot hole: The beginning of the episode shows video footage for Dick Clark's telethon of the Fantastic Four battling Namor underwater. However, the Fantastic Four didn't even meet Namor until the third episode of the series. (00:01:00 - 00:02:02)
Other mistake: This series is in the same continuity as the other Marvel animated series that aired around the same time - X-Men, Spider-Man, Iron Man, and The Incredible Hulk - by virtue of each aforementioned show crossing over with at least one of the others. However, early in this episode, the Fantastic Four receive help from the Avengers, and two of their members are Iron Man and She-Hulk. Iron Man is not a member of the Avengers in this universe, he is a member of Force Works. She-Hulk is not a member of the Avengers either. She is an attorney and is also frequently off doing missions with Bruce Banner/Hulk. (00:01:52)