Talk:True Pacifist Route/@comment-199.166.228.247-20151028033043/@comment-184.185.152.2-20151110235950

You have to reset, replay the game and after sparing Undyne, visit her house in Waterfall. The Mysterious Key does not open the Mysterious Door in Snowdin if that's what you're referring to, the Mysterious Key opens the house next to Napstablook's. To open the Mysterious Door you have to go through the Special Thanks credits after finishing the True Pacifist ending without getting hit once.