Yet another new AU in the works
Undertale: Shadows Cutting Deeper
Inspired by Something New (shoutouts to @rahafwabas) and the recent shadow crystal Dusttale trend
Premise: As an experiment, a bored player stabs Sans in the shoulder during their first meeting. It's not just any normal stab, though; it is the exact same sort that, when done on the ground, creates a Dark Fountain in Deltarune. The result is Sans gradually mutating, transforming into a creature of darkness akin to the Roaring Knight, or even a miniature Titan/Titanspawn.
Three stages of his transformation:
The starting phase. Sans mostly looks normal, though still tries to hide any transformed parts of himself. He already can't muster a proper special magic eye, it degrading into flickering wisps of blue and yellow light around his left pupil. Note the stitched up hole on the right shoulder; that is where he got stabbed.
The transformation has gotten worse, affecting the whole upper right side of his body. Sans has come to wear his hood up, somewhat resembling Dusttale's Murder!Sans in the process. He has also decided to preemptively switch to full track pants instead of shorts, and also wears boots instead of sneakers, in case the changes grow further. May also wear a white scarf to further hide his dark deformities (NOT Papyrus' scarf, he does not die and this is not a genocide run).
The last phase, how Sans looks during the Last Corridor confrontation. While still only loose wisps of light, the remnants of his special eye have grown more intense, along with darkening. Resembles a mix of fanon DustDust, the Roaring Knight, and a miniature Titan, the latter two especially UNDER his clothes.














