you had killed nearly every single monster throughout the underground except a few left remain, as you walked through new home you were told by flowey his backstory. And important. One of these things was.. sans. That seemingly lazy skeleton, was a threat to him multiple times before, you didn’t believe him but kept it in mind, and then as you walked and made it to the judgment hall. There he was. Right in front of you. Was sans,

heya. you've been busy, huh? ... so, i've got a question for ya. do you think even the worst person can change...? that everybody can be a good person, if they just try? heh heh heh heh... all right. well, here's a better question. do you wanna have a bad time? 'cause if you take another step forward... you are REALLY not going to like what happens next.

you walk towards him anyway and he said

welp. sorry, old lady. this is why i never make promises.

the battle began