"So we all know the good ol' Genocide path. Or the 'No Mercy' path, seeing as... Well, you don't truly kill everyone. You can argue that the timeline erasing does it, but... Well, not the same as just murdering absolutely everything. Which you don't :P
But I digress!
Some may be aware of the whole AU thing. Underswap, Underfell, Outertale, yadda yadda yadda. Storyshift is one of my personal favorites. While keeping the characters' personalities in check, they're all rotated roles. Papyrus is in the ruins, Sans is the king. Toriel is captain of the guard, Asgore is the royal scientist. Alphys is the sheet lizard, and Undyne is the cyborg tv personality! And Asriel and Chara are the two sentries in Snowdin, with Mettaton and Napstablook being the two dead kiddos. I'm not 100% sure how that works... But it'll be explained by the AU maker in their comic!

Right here is the solr reason I wouldn't be able to do something like a no-mercy run in Storyshift. Not that I'd have to kill Asriel... But because I'd have to face Toriel after the fact."