Dusthorror

This is a new au concept, involving the events of Horrortale happening after the events of Dusttale.
After the pacifist/rebellion ending in Dusttale, it seems that Frisk has been redeemed and will reset Dusttale back to normal Undertale. However, Frisk then betrays Sans and abandons the underground, similar to what happens in Horrortale. Sans is left underground with the dust of hundreds on his hands, left to regret what he has done. The remaining monsters eventually leave the True Lab. They try to keep as far away from Sans as possible, despite Sans no longer having any intent to kill.
Just like in Horrortale, the CORE breaks down. It takes many of the remaining monsters to find out that Sans eye, now more powerful than before, can power the CORE. They noticed Sans hadn't been doing very much other than sitting down, thinking. One brave monster went to try to remove Sans eye. Upon approach, Sans did not react. His skull was broken open to remove his eye. Sans roared in pain. He attacked blindly, off-balance and out of practice. The monster escaped with the eye, bringing it back to power the CORE. Although Sans had recovered from the insanity killing had given him, his new head wound gave him a fresh new burst of insanity. He goes to the CORE and destroys it, making the attempts to fix it useless. Despite his anger and insanity, Sans tries to refrain from killing.
The monsters are the ones that decide to start eating humans. Sans wanders around in places where there aren't many people around, occasionally stealing just enough food to survive. When Aliza falls down, Sans can only be seen in the distance sometimes and never speaks to them directly unless a genocide route is committed, in which case Sans will speak to them directly and fight them in Last Corridor.