The fight with Sans Undertale is incredibly famous. After killing his brother, Papyrus, Frisk/Chara is on their way to destroying the entire game. This fight is the thematic climax of the genocide route and all of Undertale... and it's incredible. Why is it so good? Because of buildup over the course of all previous playthoughs, incredible payoff with no disappointments, and a heartbreaking finale. Then I take a look at the apocalypse it left on the internet.

0:00 Intro
1:10 Part 1, the buildup
11:08 Part 2, the fight
28:04 Part 3, the fallout

Music (almost entirely by Toby Fox):
Another Medium
Ooo
The Choice
Battle Against a True Hero
Small Shock
Anticipation (slowed down)
It's Raining Somewhere Else
Can you even call this a hotel I mean they didn't put a mint under my pillow or anything
MEGALOVANIA
An Ending
Death By Glamour
Megalo Strike Back
Traditional Chinese Megalovania Remix (remixed by me)

The thumbnail art was primarily by wiki234, but also mintdesco for Storyshift Chara, and the Underswap Papyrus art was uploaded to the Undertale wiki by fnaflover999m