Top 10 Saddest Undertale DeathsGarythesnail I was surprised to see this wasn't a list already, so I figured I'd take action.
The Top Ten
I'm a huge fan of Undyne and she's definitely my favorite character along with Papyrus. If you decide to kill this hero, she stays determined to live on by thinking of all the people she loves. Her mentor and father figure Asgore, her love interest Alphys, her best friend Papyrus...they're the reason she's fighting, and she refuses to let herself die. As she slowly fades away, she shouts that she can't die because she must protect everyone. Along with the depressing music track that plays with it, it makes it an incredibly sad experience. - Garythesnail
If there's anybody nice enough to befriend a genocidal maniac and get them on the right path, it's Papyrus. He offers nothing but friendship and guidance to the protagonist and even will refrain from fighting him. You can spare him immediately, but killing him will result in him letting you know he still sees a shred of a good person within you. Even if you halt the route later, killing Papyrus will cause both Undyne and Sans to despise you(more than usual in Undyne's case) - Garythesnail
The True Pacifist route is by far the most enjoyable way to play Undertale. You free all the monsters and give them their happy ending-that is, except for Asriel, who's doomed to be trapped in the body of a flower for what seems to be forever. As much as fans hope, there doesn't seem to be a lot of hope for poor Asriel. - Garythesnail
Fun Fact: if you kill only Mettaton, or cause Mettaton to become the ruler(by killing Toriel and Undyne), Alphys kills herself. (Not really "fun", to be honest) - Garythesnail
This one is absolutely the saddest death to me
That look on her face.
This is why you only play the True Pacifist Route. - Martin_Canine
"Y...you...really hate me that much? " - Garythesnail
Sans is pretty overrated, but his death was still pretty sad. "papyrus...do you want anything? " - Garythesnail
By killing Flowey, then going back to Asgore to fight again, you can as usual spare him or kill him. Sparing him is the right thing to do(even though Flowey kills him anyway), but if you spare him after following the pattern I mentioned, he will give you his own soul, thus ending his life. In any route except True Pacifist, Asgore is tragically killed and thus causes devastation in the underground. - Garythesnail
"This world will live on..."
Maybe the genocidal weed deserves to be killed, but at the end of Genocide he realizes he's Asriel and begs you not to kill him. Spoiler alert: you have no choice, and must kill him. In what may be the most brutal hits in the game. - Garythesnail
Not very sad, but if you kill Muffet then a spider will crawl onto the spot where she died and leave a rose. It's kind of sad, really.
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List StatsUpdated 23 Jun 2017
192 days old
2. Papyrus (Genocide Route)
3. Asriel Dreemurr (True Pacifist)