What is underfell, what is underswap, and is fellswap common too? Like do they have planned out au stories that everyone generally follows (as consencus) or does everyone make up their own. Sincerely, a confused person who just searched undertale for the first time on tumblr looking for a cute phone background but instead found a bunch of au drawings.
((FIRST OFF—I just gotta say that I hecking love your icon my dude!
Though I maaay be a little biased because Ryan’s my fave LMAO
In any case, Underfell, Underswap and Swapfell–as you’ve probably already gathered–are all AUs! Arguably speaking, Underfell and Underswap are some of the ‘big’ ones while Swapfell is relatively new and not as established beyond headcanons about the skelebros (at least on tumblr; originally it was centered around Alphyne by the original creator but then it got kinda derailed along the way by the fandom LOL)
Underfell was originally created by two people who have since let the fandom have full reign of it and locked up the hub blog for it (not mentioning their URLs because they said they no longer wanted to be associated with the AU). Originally, Underfell was meant to be ‘evil’ Undertale, but then the creators decided that it would be more fun to make it a design-only AU. This meant that everyone was free to use the original Underfell designs however they wanted and with whatever story they liked. The only set ‘thing’ about Underfell from that point on was that everyone looked edgy. :’D Other things that are considered universally accepted fanon lore for Underfell that don’t relate to appearances are things like Sans calling Papyrus ‘boss’ and having a taste for mustard as his condiment of choice.
Underswap was originally created by popcornpr1nce with the designs in this post. There used to be hub blog with information for this AU as well but that has also been shut down for a while now and, as far as I know, popcornpr1nce has since let people do their own thing with the AU. Underswap is essentially a swap of some of the more prominent roles in Undertale. So Swap!Papyrus takes on the role of Sans and is the one you fight at the end of a No Mercy run, Swap!Toriel takes Asgore’s place in the castle, Swap!Undyne takes Alphys’s place in the labs, etc. You can see most of the main swaps in that original picture but there are some more obscure ones (such as Gaster and Riverperson swapping) that have been kind of lost to the fandom since the hub blog went down.
Swapfell was originally created by kkhoppang who has since deleted their blog and also their twitter I believe ;m; I don’t have a link to their original line-up of character designs but I do have a couple other links to their Alphyne designs (along with some Tori and Napstaton <3) and their finalised versions of what the skelebros would look like. The designs you see floating around tumblr for the bros now are a popular fanon version that sort of took over after kkhopang left and aren’t actually anything like their original version. In any case, the idea of Swapfell was basically taking the Underswap universe and making it ‘edgy’ like Underfell and thus combining the two AUs into one. I actually don’t know much else about the AU in general—not in the least because I can’t speak a lick of Korean so I don’t know if there was ever any lore associated with kkhoppang’s pictures or not ahahahha
So, as far as stories go, Underfell and Swapfell have no set stories and everyone is free to sort of do whatever they like with the AUs, though most people typically keep in making it follow Undertale’s general story with the additions of a little more angst and violence LOL Underswap has more of a rigid format in that, beyond the swaps, the story stays the same as Undertale, but many fans have done creative twists of their own and really made the AU into something fantastic as well!
In the end though, honestly, you should feel free to interpret the AUs however you want and however you most enjoy them! If you’re new to AUs, it might seem a little off-putting or even over-whelming at first, but it can be a lot of fun to dig into them if you find people who do it in a way you like! And if you don’t like anything already made, there’s always the option of doing your own version! :’)
Anyways, I hope that was informative and, also, I hope you eventually got a sufficiently cute phone background!! <33
And if you ever need help on that note, totally IM me dude and I will hook you up because I’ve been hoarding pretty fanart for aaages ;3))