there is so many levels to how fucking iconic the sans battle is i could write about it forever
-comedic relief turns into most difficult battle in the entire game
-every single aspect of the battle bends the conventions of game mechanics and sans is doing it On Purpose https://twitter.com/finnmertens/status/1306084361352089602

-the killing blow is a secondary strike that sans didn't expect to have to dodge (because despite bending the game mechanic rules, he's assuming you're Playing By Them), where who I believe is Chara (not Frisk or The Player) finally snapped completely n decided to cheat themself

-Sans alludes to a L O T of undeciphered worldbuilding and lore that still hasn't been fully explained despite years of theorizing ofc but it keeps me up at night
-it is actually very heroic and very SAD; sans is too aware to not know it is a stalling battle, not one he can "win"

he's doing it because he felt helpless before but realized it's better to take a stand than simply watch the world die
-megalovania being "technically the players anthem" but sans being so heroic and badass that it became HIS theme thru people's interpretation is INSANELY COOL

-> adding to the chara killing blow thing; it's The Player's actions throughout the game that lead to chara losing their grip on hope and reality and becoming what they inevitably become, so in THAT sense it is still thru YOU, THE PLAYER's actions that ends the battle. it is SAD

if you're interested in the Chara Is The Narrator theory THIS is my favorite summation of the evidence cuz of how detailed it gets. its like, super long. i love it. https://determinators.tumblr.com/post/159674581147/greetings-uh-so-ive-been-working-on-this

It becomes a lot more clear Why Chara does what they do over the course of the bad route as a three-dimensional character. I think it adds a lot of interesting context to Sans's battle; forcing Chara to be the villain and forcing Sans to play the hero, and that final kill.

It also makes the True Good ending and that hug with Asriel all the more sweet....but im getting away from the point of this thread haha. UNDERTALE GOOD.