X-Men #35: Along Came a Sales Gimmick

X-Men #35 is a wholly gratutious Spider-Man appearance - the first, no doubt, of many. It ostensibly advances the Professor X plot, as Banshee reports in with the X-Men to notify them that he has found Factor Three's base, and that they should beware of a "Spider".

Without even the thinnest rationale, Peter Parker just happens to be visiting Westchester County, and encounters the real "Spider" - a metallic roboty thing. Due to a hilarious misunderstanding the X-Men believe that Spider-Man is the "Spider" they should be wary of, so they come to blows (well, blows and optic blasts and ice bolts and big hairy kicks and webshooters...). Parker mostly holds his own, but it's not exactly a gloves off fight. It's a bit sad when you think about what amazing friends they should be instead.

Eventually, the error is revealed and they make their peace. Unusually for this type of story, they do not then immediately team up and take down the thing that has set them against each other. Instead, Parker goes home to New York - and the X-Men are left with a lead that Factor Three are at a central European mountain range...