As hundreds of genocide timelines went by sans could feel his sanity fading with each timeline and knew he may snap soon if something doesn't happen then he noticed something while he was in the last corridor "I thought there wasn't any bats in the underground? though this just might be enough to tip the fight in my favor" sans then proceeded to absorb the soul of the bat "in a way it feels odd I feel more powerful but like something is missing that would truly boost my power" unknown to sans after he absorbed the soul of the bat he grew vampire fangs and his right eye now faintly has the image of a bat and just like the previous timeline he died but when the timeline reset he finally snapped and when he looked in a mirror he noticed the changes to what he looked like and then decided something "if me snapping is what frisk wants then perhaps a bad time isn't enough and they clearly are having a "mad time" doing all this genocide I'd even say they enjoy it so it's time to show them the consequence's of there actions it's time to show them an eternal mad time that they will never recover from"

his eyes began to ominously glow red with purple outlining the red glow he then teleported into the entrance of the ruins and walk to toriel's house killing every monster he came across and it seems that frisk hasn't even arrived in the underground yet so he found and killed all of the monsters in the ruins it hurt sans killing toriel one of his only friends sure he didn't exactly enjoy killing the other monsters but it hurt a decent amount more because of there friendship reminding him why it needs to be done he felt determined to end this cyclic of genocide and he would do so by any means necessary next he encountered a very scared Flowey who just now noticed what was happening "pleas don't kill me" sans pulled Flowey out of the ground with telekinesis and shot him with a few gaster blasters "sorry today I'm all out of mercy" and to the slight surprise of sans Flowey was killed in one hit almost like Flowey had some levels of violence and sans after each kill could feel his power rapidly rising his determination growing his stats increasing he needed more of it

as he arrived in snowdin he could see signs of people preparing to evacuate and he couldn't allow that so he killed all the guards he could find killed all monsters he encountered killed the shop owner and everyone who stayed in there houses he was certain he got them all then he found his brother papyrus he was trying to get sans to stop to calm down and explain himself sans even considered sparing papyrus for a moment but in his head was echoing why he was doing this and after he killed papyrus it hurt him more and was losing more of himself to his madness and he grow more determined to complete this so he never needs to again and reminded himself he needs to try to hold onto some kindness so he will remember to attempt to fix this afterword's just after he was thinking about that he noticed that papyrus has become a ghost