Board Thread:General Discussion/@comment-28850001-20160626050029/@comment-5956954-20160626053251

Then that means you cannot get the letter. You see, when you play the game the first time, it will always be the neutral route. If you beat the neutral route, you can do the true pacifist route, which is simple if you were already a pacifist. Continue from your last saves before Asgore and travel to MTT Resort, and the phone calls should guide you. If there are no phone calls, you didn't befriend Undyne or Papyrus, or both. Befriend Undyne and she will give you the letter when you exit her ablaze house.