Lots of spoilers ahead, no way to avoid them, so here's a warning that is hopefully long enough to fill up the preview from the main page AND make sure everyone sees it.
So I'm specifically talking about the "Toriel - Family" ending, a.k.a. Flawed Pacifist. I know you have to befriend both Papyrus and Undyne - and if you kill anyone after befriending Undyne, you'll get the "Toriel - Betrayed Undyne" ending instead, and if you kill anyone before befriending Undyne, you can't befriend her. There are two branches to the Family ending, one where Alphys is even more withdrawn and depressed - if you don't date her - and one where she's happy and looking for a way to help monsters escape the Underground without having to kill humans - if you do date her, and the ending I want to get.
So, backstory out of the way... If I don't kill any monsters at all, and I befriend Papyrus, Undyne, and Alphys... won't I get the Pacifist ending instead? Do I need to do another Pacifist run to enable a True Reset so I can get the Family ending? Or is there a way to befriend all three of those characters, not kill any monsters, and still get the "best" Neutral ending?