The sound effect used for Magneto's magnetic powers is the same sound effect used for the Klingon cloaking device in Star Trek III: The Search for Spock (1984).
Because Mr. Sinister had such a complicated design for the animators, could not do a 360 degree turn when animating him.
Sidney Iwanter, an executive at Fox, originally planned on "ending" the series with a big bang ("Beyond Good and Evil - parts 1-4"). They even had planned to have characters leaving the team at the conclusion, but at the last minute Fox asked for more episodes. Unfortunately, at the time Marvel was filing for bankruptcy and could not afford to produce more episodes, so Saban funded them directly. This explains why the last six episodes looked different than the previous 70. So the show officially "ended" things again with Graduation Day (1997).
As of July 2022, the series is put in story order on Disney+, meaning episodes that aired later that were meant to be after specific storylines are now where the creators meant for them to be.
Fox initially had a lot of resistance to the cartoon series before it became a success. They felt that the target audiences, kids under 10, wouldn't be interested in a romantic love triangle between Cyclops, Jean, and Wolverine. They also thought kids wouldn't keep up with a show that was serialized.