Mojovision - S2-E11
Deliberate mistake: Some of the footage of the X-Men in action that Major Domo shows Mojo is clips from previous episodes, and even clips from the show's opening theme. (00:03:36 - 00:04:22)
Starring: Alyson Court, Cathal J. Dodd, George Buza, Norm Spencer
Mojovision - S2-E11
Deliberate mistake: Some of the footage of the X-Men in action that Major Domo shows Mojo is clips from previous episodes, and even clips from the show's opening theme. (00:03:36 - 00:04:22)

Slave Island - S1-E7
Plot hole: After Storm's attempt to escape the Genoshan prison is thwarted, she ends up in the ocean right at the shoreline of the beach, where she is captured by a Sentinel. Aside from the fact that it makes no sense for a Sentinel to be hiding in the ocean in the event that a mutant tries to escape the prison, there is absolutely no way that a two-story tall robot could hide in the ocean right by the beach, as the water would be way too shallow. You can even see that the water level only goes up to the Sentinel's ankle area when it is standing upright in the ocean. (00:03:15)
Suggested correction: Perception. (1) The Sentinel isn't as close as it appears. If it were close, then she would have been caught in its waves as it emerges. Also, she would be looking only at its chest circle. It's several yards away. (2) She washes ashore. She fell from the sky. She couldn't have fallen from that great height into shallow water without hitting bottom. (3) It's also a two-story tall robot. Its weight would sink it into the sand. So it could have very well been down that deep.
Sentinel never sank into sand in other episodes.
Well, it's shown here.
General Chasen: Since your defection, we've tried repeatedly to duplicate the process that created your adamantium skeleton. The results have been less than encouraging. We brought you home to find out how you managed to survive the process.
Wolverine: I survived it because I'm a mutant, you dimwit! (00:13:29)

The Juggernaut Returns - S3-E17
Trivia: When the new Juggernaut crashes through the film studio, the production being filmed is a parody of Mighty Morphin' Power Rangers. There is even a short musical phrase similar to MMPR's theme song. (00:16:10)
Question: Does anyone know what the Russian writing says on the wall behind Omega Red when he is standing at the podium and talking about the return of the Soviet Union? (00:15:08)