In the story, the player does a geno run and resets, but the game is a buggy and broken version and everyone remembers, then sans and alphys confront you in the last corridor and before sans dies, alphys gives him determination so he can last just a bit longer, after that sans dies fully and gets put in intro panels (specifically the one with mount ebbot) of the game due to the glitches and bugs getting worse and gets stuck in one, causing his colors to take that of the panels (he eventually escapes)

In order, these are the sanses:

S-000 (the sans that had determination): His left eye is scribbly and weird, his right eye is scratched out with yellow and some blue, and as mentioned before, has the intro panel colors. he appears not as melty and has his wound from the fight (no blood tho) but when his “eye” (a yellow diamond shape with hibts of blue) is activated his right eye loses the scratch, and his face looks melty.

S-001 (just my error take): After 000 escapes the panels, he tries to make a sans using leftover data to replace him while he looks for the source of the bugs, however, something goes wrong and it creates this guy, at first, he didn’t have his other stages and was just a “normal” sans, but as time went on, he started losing his mind more and more, as he could see the bugs better than the others, causing him to gain his other stages, and he becomes error.

S-002: Another attempt by 000 to make a new sans, this one succeeds and 002 is just a normal sans