I Can Rock w It
So, the -cest suffix has fallen out of favour in fandom spaces... Good riddance! But I definitely won't be replacing "selfcest" with "self love," and I'm only lukewarm on "mirror shipping." Luckily I don't talk about Sans/Sans pairings enough for this to matter to me. I'm only invested in a few of them.
Like... Kustard! People are always drawing those two (Normal Sans Undertale and Red Sans Underfell) together. Make them a trio with Underswap Sans (Sans but Papyrus flavoured) and they're even cuter! I like Dustard, too, since Dust's (Sans but a serial murderer) edge is even sharper than Red's. I'm sure the work of one of my favourite artists, GOKIN, convinced me to ship it. And after watching some animations by Peng2_comics... yeah, I'm here for life.
(Maybe don't click that link unless you like skeletons. Definitely don't click it in public.)
The fanime Underverse popularised the grouping of "good" and "evil" Sanses, too. Lots of people on my side of AO3 are especially enamoured by the bad guys. I see them shipped with each other, as a harem for the reader-insert, or both at once. I'd join the fun if I was more interested in the interdimensional-crossover multiverse-travel thing that's so beloved these days. It's not my thing, but I'm not knocking it, either. The world runs on pleasures as simple as recolouring Sans the Skeleton, changing his whole personality, and mashing all the new characters together.
Do these fan characters need to be called Sans? Probably not.
Isn't it weird how much they overshadow the original? Probably yes.
Is this "ruining" the UNDERTALE fandom? Well... take it or leave it— this is the UNDERTALE fandom. I'll enjoy what excites me and ignore or endure the rest.
Dreamtale, for example. Apparently Charasriel wasn't enough for us and we needed the exact same story again, this time with skeleton brothers... both of whom are Sans. (Papyrus: shortchanged again!) Is it more accurate to call them Sans-shaped creatures? Because the rounded, smiley skeleton base is where the similarities end. The story strips Sans of everything that makes him unique, nuanced, lovable, and cool, then shoves his conceptually-naked likeness into a generic narrative of good versus evil.
And neither new version of him is hot!!!! Dream (Sans but he's a Madoka-expy god of "positivity") never made it onto my radar. He's so, so, so not my type. Nightmare, though? (That's Sans but he's a tentacle god of "negativity.") He's the leader of the Bad Sanses. Dust is popular enough to be included in this beloved crossover cluster, but not popular enough to have many fanfics set in his actual universe.* So I'm only ever searching for my psychotic sweetheart when this ugly, goopy guy plops his overly formal ass directly on my radar. Ugh. I get so turned off that it wraps around into kismesitude.
* For reasons I've yet to analyse, male fans love DUSTTALE a lot. They create countless "takes" on that AU, none of which involve Underverse-type crossovers. I know why female fans love the crossovers (one word: shipping) and maybe dislike DUSTTALE proper (ten words: everyone is dead and Sans is trying to kill you) but... yeah. It's just interesting, the dichotomy.
Ultimately though, it makes me laugh. I refuse to feel angry about any of this— firstly because it's unhealthy to get mad on the internet, secondly because I value everyone's fun equally. There are Sansgirls who wouldn't like or understand what I'm up to with Gokiburi-chan. I wouldn't want them coming into my house to criticise me, so why would I do it to them? Golden rule, everybody.
Speaking of Goki-chan, the best Sans "mirror ship" would need to include her. Sans, Red, Swap, and Goki sounds like a solid OT4. I'm not sure what cliche I'll use to get them all into the same universe... but it will surely affect Goki's characterisation. Her personality can change a lot because of her circumstances, especially how well received she is by her beloved...s. Plural. In this story, she'll pursue all of them equally. Three times the rejection!