When did Mr. Sinister first appear in the original X-Men cartoon?

Does anyone remember the cool, original X-Men cartoon? I’m dying to find a clip, or, better yet, the whole episode in which Mr. Sinister first appears on the show.

If I remember correctly, he first appreas at the end of an episode, where he is creepily watching a conversation between Cyclopes and Jean Grey. If anyone can help me out I’d really appreciate it.