A bit.
Flowey will know you killed people (as far as I'm aware) and others may experience a bit of deja vu.
If you stop before selling your soul, you'll be fine.
I have a rule for this: If I'm currently involved with it(whether it's a game, anime, or whatever). Don't do it. Wait until you've finished it, and lost a bit of interest. Then go for it. Go for all of it.
For the sake of completion and learning about the world of the game I kinda want to do a genocide run now that I did the pacifist run, but at the same time I REALLY don't want to :c
genocide run does a lot of explaining about why flowey does what he does, also for most of it, it's actually easier than pacifism, except for two bosses who will not be named.
Actually, it doesn't really explain anything about Flowey that Pacifism doesn't, at least not if you go back and talk to Asriel, at the flower patch where you fell down in the very beginning.
At the end of the Pacifism run, if you do everything you can to show him mercy, he will be tending to the flowers that dampened your fall at the beginning.
When you talk to him repeatedly, he tells you a lot of things:
That Char/[Insert character name]/The First Child was similar to you in a lot of ways, including your clothing.
That he was imposing his memories of Char on you.
That Char was an awful person that hated humanity.
And that when he absorbed Char's soul, it was Char that made him carry the body to the surface and wanted to use full force against the humans that attacked him. He also says that his own choice not to harm those humans, which led to his death, was what caused his belief in "Kill or be killed" as Flowey.
And that he is happy you were not like Char.
at the part where all those monsters are telling you about asriel and the first human to fall down, because everyone is scared of you it's flowey talking to you instead and he pretty much says "i bet people are watching you do this right now because they are to scared to do it themselves"
I COULD COMPLAIN ABOUT THERE BEING A FAKE PAPYRUS IMITATING ME, BUT I THINK I'D MUCH RATHER SIT BACK AND APPRECIATE THE FACT THERE IS SOMEONE WHO HATES JUNIOR WORD JUMBLES AS MUCH AS I DO!
So I'm curious about something; any of you guys ever tried doing a Genocide run except sparing Toriel? I imagine that would probably cause a special ending, given the utter cruelty of it, but I do not have the skills or patience to try it.
Sans tells you to go to hell when you get to him, but he doesn't try to kill you. At the end of the game Sans goes to live with Toriel, but he can't bring himself to tell her all that you have done. They live in the ruins and never leave.
This game inspires me to learn how to draw just to make fanart. Jesus this is gonna be a hell of a ride. This game is my life right now, and most likely will be for about the next 2 months. So let's keep it coming.