http://breezewiki.catsarchywsyuss6jdxlypsw5dc7owd5u5tr6bujxb7o6xw2hipqehyd.onion/undertale/wiki/Sans
Regardless of the human being partially or wholly merciful, Sans tells them that if "the old lady" (confirmed in the True Pacifist Route to be Toriel ) had not made him promise to protect them, " (they'd) be dead where (they) stand. " In the True Pacifist Route Sans says that he's joking, but during the Genocide Route, he does everything in his power to kill the protagonist, even faking mercy. Sans may have a scientific background. Evidence includes the quantum physics book, his workshop ,...