Save Point

Saving is how a run of Undertale is recorded and resumed, and the game folds it into its story. After a Neutral ending the player can reload their saved game; if they killed no monsters before that ending, the reload leads on to the True Pacifist ending. Inside the story, the power to save and load belongs to Flowey before the human arrives: it lets him act outside the laws of the universe. He gets that power back at the end of a Neutral route, when he kills Asgore and absorbs the human souls the king had been collecting. Sans also breaks the fourth wall now and then, hinting that he understands how the player manipulates the world through save files.