Not sure if this idea has been said already. I'm on mobile currently, so not too much but I really want to see an AU where instead of the underground, all the story is inside a gigantic castle ruled by Asgore. Toriel would be around the castle before you start the actual story (e.g. outside the ruins) and would technically be a character who went rogue frome the castle. All major characters would be royal guards, or, in the case of Alphys, would still be a royal scientist. They would be monsters, and Frisk a human as always, and although many think Frisk just wanted to become a royal guard, no one actually knows why she stumbled in the maze-like castle. Undyne would be captain as always, and Sans would be on par with the level of authority as a royal 'guard'. Flowey would be one of those castle rats, knowing all around, about, inside out of the castle grounds. Genocide would be considered to castle residents as Frisk coming in the castle to assassinate everyone. Pacifist, no one knows. Just an interesting AU that popped up in my head. Truthfully though, I just want to see Sans in (light) armour. Hehe sorry!