Notes:

What I'd imagine sans would say if you played a genocide run legit and somehow cheated for only his fight (maybe hacking in some Temmie Armor?)
or
you got to his fight, lost, and somehow went back to change it to a neutral run (like if the last save was from before killing the last monster outside Mettaton's boss room – would that actually work?)
OR
you completely gave up on a genocide run after losing to him and resetting.
It'd be even more meta (and impossible) if it could check your browser history to see unscalable mountains of p--- if you looked up his fight on Youtube and/or the genocide ending when you've given up on doing it yourself.

PS) I found a plugin for Paint.NET that lets me open .gifs as layers and save them as .gifs (though the quality kinda goes to s---) without manually saving each layer as an individual image and using something else to animate them.

This (and some other stuff) is just one of many things I've made and never got around to uploading.