this is a episodes of Undertale, when everything is gone really dark, sans just went missing to do this, for their own sake, he says "i just want to commit suicide, before something happens in my head, you'll know what gonna happen next, you don't know where you are.", then sans just killed himself with his bone and slash his head before he went dead, and the shadows tooks in, monster kid was looking for sans is like "Man, I hope the dude was alright, I guess I just walked to Snowdin...", then he walks in, monster kid talks before sans was just covered with dust "Hey dude, sans, it's that you?", but no one's listening to him and he talks nicely, "c'mon kid, it was just a setup alright? let's go to my home, it will soon there." then monster kid talks with sans "I'm so glad that I found you." then sans went a dark side on him "let's go kid. =)", then monster kid walks towards our home, "Hey what happened to you Sans, and where have you been all this time?", then sans had a dark expression on his face, his grin went crazy and kills monster kid, papyrus just warned over the population of the monsters goes to evacuated, Undyne is in charge, then papyrus says "I THINK MY BROTHER HAS GONE REALLY MAD, I THINK HE JUST KILLED ALL THE MONSTERS. OH NO, HE IS COMING BACK! I HAVE TO HIDE!" then papyrus inside and hides on his room, then he escapes, and talks "I NEED TO TALK THE OTHERS ABOUT THIS...", then sans walks in "hey paps, how are ya? you just have to find something else?", then sans and the shadow figure appeared, he just runs away.

@Mr_gold_lover