True Pacifist Route

The Pacifist Route is one of the three major Endings of Undertale. It is inaccessible until the Neutral Route has been completed without killing any enemies

Method
The Pacifist Route, assuming a Neutral route with the correct requirements of having killed no enemies (Note: Killing Asgore or Flowey at the end of the Neutral Route do not impact this requirement) has been just completed, is acquired by following the hints provided by the phone call that Frisk receives after the credits. By reloading the Neutral Route save file and befriending Papyrus (via the date at his house), Undyne (via hanging out at her house/giving Alphys the love letter), and Alphys by completing the True Lab after delivering the letter, the player can fulfill the requirements for the Pacifist Route. On trying to leave the True Lab, the player will hear a mysterious voice, and then be teleported to New Home, with the elevator exiting to the core vined off. By proceeding forward and confronting Asgore, the Pacifist Route can be completed.