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).
On November 2021 Disney announced they will be reviving X-Men the animated series under the title X-Men '97 (2024). It will act as a follow-up to the conclusion of the original series, with some of its original cast returning.
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).
Because Mr. Sinister had such a complicated design for the animators, could not do a 360 degree turn when animating him.
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.