Oh man, I could take a whole series of X-Factor teleporting into random series, causing mayhem, and then teleporting away.

I was thinking that exact same thing. Pretty much *anything* plus X-Factor is win :)

Although I like the idea (like in this story) of them not quite on-panel, arriving just after or just before some canon event and getting out before they've created too many complications. You could have a running gag of them always *just* getting out before the real heroes of the story trip over them XD