The Underground where magic, morales and respawning rules

Undertale. The best Indie game of 2015, where you control the child of peace, or the child of chaos. And not to mention the Fandom that came with it, which there is a few great stories that I have read.

That aside most of you know the plot to Undertale, hopefully. If not, then let me explain.

Undertale starts off by telling us the story of the monsters war against the humans that ended in the monsters being trapped underground by the barrier. The barrier is a magical seal that can only be broken by 7 human souls or exited by a human and a monster soul fusion and it can be entered by anyone.

That's the gist if it, and the child itself is gender neutral but commonly referred to as a female for their name. Frisk. Here's the most important parts for this branch, should you go down the pacifist route where you spare all or most of the creatures and monsters, or the Genocide route where you kill everyono?