Triplecide

Triplecide is an officially outdated AU in which Sans takes Frisk's SOUL. Actually hold on I'll just write the dumb story.

Story
While in most timelines, it takes hundreds of resets to change an outcome, one instance of a clever Sans resulted in a change after just three.

When the human completed Pacifist a couple times, they, naturally, got bored with the world and took a bit more of a "soulless" approach. They'd kill everyone, rather than saving them. This didn't seem too bad, however. After all, resetting would just fix everything, right?

Well, the human did a Genocide run, killed Sans, all that stuff, you know the drill. After this, they didn't have too much control over themself, and on the second Genocide run, Sans noticed something was unnatural about the human, even more than before. So they completed another Genocide run, possibly against their will. But this wasn't over, they were gonna try over and over, doing it again and again, Sans had to stop this garbage.

So, Sans had an idea. The other humans lost their SOULs, right? So it isn't impossible to kill them without them just coming back. So what Sans decided to do was kill the human without even starting a battle and taking the SOUL for himself. When the genocidal Frisk walked up to Sans he just straight up killed them without any speech or anything and yanked their SOUL.

But Sans knew if this SOUL broke, the human could just come back and redo everything. Somehow. So he had to keep it safe. Sans absorbed the human SOUL. Maybe on accident I don't really remember. Either way, he did. This changed something fundamentally about him, and, with this power, he transported to another world. Another timeline. Yeah he can just do that, how else would he be a Roblox OC. He's an AU Wanderer.

Oh also the situation made him a bit more grim in personality than normal Sans and for some reason absorbing the SOUL gave him sharp teeth and ripped up his hoodie and turned it like kind of lavender. No idea why. He can unabsorb Frisk's SOUL at any time, keeping it in his hoodie otherwise so it stays not broken. When he does have the SOUL absorbed, not only is he more powerful, but also he loses half of his body to Frisk, who then controls it. He was dubbed "Trip!Sans" or just "Trip" as a shortening of the AU's name.

The AU was cancelled in 2020, to be rebooted to make a little more sense. This, like Erased.'s concept, didn't just delete Original Trip though. Instead Frisk's SOUL was sent somewhere else and Original Trip was made into a meta character in a sort of Error Sans kind of way, viewing the game's code and the GUI's and all that good stuff. Who knows where that dude is nowadays. Hope he's doing well.