Did you know that several episodes of "XMen: The Animated Series" have more than one version? From animation corrections to redubbed voices, this video compares some of the episodes that have had changes made over the years.

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You can watch the entire twopart pilot as it originally aired here:
https://archive.org/details/xmen_202402

Disney Plus and the DVD set both have Iona Morris as the voice of Storm in season one. Fandango At Home (formerly Vudu) has Alison SealySmith for most of these episodes. (I think the pilot part one is always Iona Morris, I don't think Alison rerecorded that one.)

Disney Plus and the DVD set both have the original, uncredited Mr. Sinister voice in the season one finale. Fandango At Home (formerly Vudu) has Chris Britton's voice.

I don't know of anywhere that you can see the original ending of "Slave Island" in high quality. It is not on any of the DVD sets or streaming services. I found it via this video    • XMen The Animated Series' "Slave Isl...  

As I mention in the video, Disney Plus has the original version of "No Mutant Is An Island," and they have it in season three where it belongs. This is true of Fandango At Home (formerly Vudu) as well. The DVD set has the redone version and they have it in season five where it aired.

The site that first brought all of this to my attention is DRG4's XMen page http://drg4.dancemaniaex.com/x.html