Undertale: Twisted is a take on Taletwist. Monsters were never sealed away, or even had a war with Humans. Monsters live on their own continent in the world, somewhere near Australia. They’ve been a part of all major and minor important moments in history.
Papyrus was a medic in World War II, and one of the greatest soldiers in monster history. Legend about his amazing capabilities and his will to continue on are told trough historians to this day. Sans is his grandson rather than his brother, and Semi is his brother instead.
Frisk is a talking protagonist. They're cousins with Chara and a big fan of Mettaton.