This is the famous story titled, “Slumber party!” Professor X lets the New Mutant girls have a sleep over at the mansion with some nearby locals.
It’s more than a little odd that X would let normies come to the mansion, given as how it gets attacked so often, but at least one of the guests is Louise Simonson (Walt Simonson’s wife, seen reading People magazine.)
Also at the party, the kids put makeup on Rahne Sinclair, and she kinda has a breakdown because of it. It’s developing her Scottish/religious morality–a nice character development sequence.
And, of course, something unexpected happens. Warlock arrives, and we learn that his power is to drain the life out of Earth’s organic matter.
He also seems unable to differentiate people from devices, as he talks with computers and thinks a refrigerator is a “person” that stores other organic creatures within it. It’s fun and cool and Bill S. is the perfect artist for it.
The New Mutants take a liking to him, and invite him to stay. He even got to appear in the corner box.
Creators: Chris Claremont and Bill Sienkiewicz