I thought itd be fun to share some Undertale AUs i thought up of, so here goes!
I havent fully figured out everything with the AUs, but these are the protagonists of Undertale Pink and Undertale Grey, two AUs taking place after the events of Undertale. Both Lima and Marty are the 8th fallen child, but taking place after different endings that take place in Undertale.
Undertale Pink is an AU where an 8th fallen child enters the underground after one of the many neutral runs of Undertale, and the main idea is that you get to choose what neutral ending you want to start off from, after a brief conversation/character creator with Flowey (who's incredibly surprised to see you.) Lima is one of the very few remaining humans who can cast magic after so many years, so a lot of their puzzles and combat encounters revolve around casting spells and the like. I also imagine that the route you take in Undertale Pink is the exact same one that Frisk takes in Undertale, but due to all the different possible endings, the route will feel drastically different each time you go through.
Undertale Grey is an AU where an 8th child falls into the underground after the true-pacifist ending, where most of monsterkind has moved to the surface and the underground has been left as a museum of memories. Not really any kind of dark or moody game, but a much more somber and bittersweet tone. Marty would likely not directly fight any monsters, rather go on fetch quests between each area in the game, with them befriending all the monsters that remain. In a more neutral run, you ignore everybody, or you go out of your way to try and entomb the underground again. After all of your quests and wanderings around however, you would eventually meet Flowey in New Home, bittersweet about all of his compatriots on the surface living good lives. You get to know him a little, before he waves you off and lets you do whatever you wanted to do.
i really want to try and explore both of these AUs a bit more, but i wanted to share my thoughts and these cute lil fellers to try and get this stuff out there. also have a quick bad sketch i made of the two of them hanging out together :)