UNDERSWAP version of Last Breath™ Inc. with many different leitmotifs and a timeline break from the RiverPerson for Courier/Papyrus and a revival of Sans and Alphys...

Well, coming sooner or later.

Lore: In an UNDERSWAP Genocide Route, Swap Temmie brutally kills Swap Sans with the aid of Swap Chara/Frisk. Poor old Swap Papyrus notices and decides to plan what revenge looks like. Papyrus gives way too much mercy to Chara/Frisk and gets hit with the FIGHT button... but he still doesn't convert to DUST because the Swap RiverPerson manages to keep Papyrus's SOUL working. The RiverPerson helps Papyrus subtract HP from Chara/Frisk, but still doesn't kill them because Papyrus hands more mercy for some reason. The RiverPerson eventually takes Papyrus over and decides to try to obliterate Chara/Frisk as hard as possible. Even that doesn't work, so later on the RiverPerson decides to summon timeline breaks where alternate universes collide and bring random characters to continue the pain for Chara/Frisk and Temmie.