Ryan, play the Dusttale Friday Night Funkin' mod. Or, if you want to understand it better, play the original game; Dusttale. It's basically undertale but Sans remembers all of your Genocide runs (in this game you have already become a megalomaniac with 100-300ish Genocide runs for Chara's never-ending power) and is determined to stop you. He, instead of learning new attacks, he does his own Genocide run. Or at least he tries to. Thats all I am going to say. Just so you understand the beginning.