Basically, I'd written (and maintained) a list of all the mutants in the Marvel Universe up that point (late 80s, and yes, including Krakoa the Living Island) and used it in a mental experiment. The day I started, I would put the name of each person I a talked to in turn next to the mutants on the list, in order. And then I would imagine them having those mutations (powers and occasional deformities) so that I, in effect, was a mutant in a mutant family going to a mutant school.
The mnemonics of it were to keep running these parallel lists running in my head, with the people around me acting as visual aids. (Yeah sorry, people of my youth, you were glorified flash cards, which is probably why we don't have a relationship now.)
Sadly, I've lost the list on paper and I don't remember what powers anyone but myself had. I'd put Professor X at the top of the list, and figured I'd talked myself into doing on Minute 1, so I'd get the telepathy. And I guess I figured that telepathy was someone "triggering" mutants. It had its own head canon.
And this wasn't even the first time I transfigured my school mates into super-heroes...