There stood a deformed, glitchy husk of W.D Gaster, who also took possession of him, then and there. During this genocide, Papyrus found a grey door in waterfall, and stepped inside. Papyrus, now partially possessed by Sans, was forced to brutally murder EVERYONE. This is when Papyrus experienced mixed emotions Anger, Sadness, A sick sense of joy. Before Sans could turn to dust or reset, his soul fused with Papyrus’. But not before his bone went into Papyrus’ skull. When insanity Sans had pinned down Papyrus, about to puncture his skull, Undyne managed to fatally his Sans. Sans immediately resumed his fight against papyrus, while undyne attempted to strike him down from behind. When they returned, Sans had already murdered the residents. Countless monsters being slaughtered was enough to get here attention. Papyrus ran like his life depended on it, which it did, all the way to waterfall to talk to undyne. Papyrus yelled out for help as Sans chased him down the town, where he managed to lose sans to the crowd of snowdin residents. He saw his brother and ran after him, wielding 2 sharp bones, ready to torture Papyrus. He killed everyone in the ruins, he killed flowey, but the torch of insanity would pass on when he got to smowdin. He repeated this cycle 359 more times, for a total of 360 massacres. And so, he committed genocide for no reason other than satisfaction. Sans had been tainted with the DT's lust for power. What turned him into this mindless beast was none other than a failed experiment of Doctor W.D Gaster, who had attempted to give monsters the same powers that humans had. Insanity Sans was a cold blooded maniac, who killed all of his friends for an unknown reason.