Mysterious Door

The Mysterious Door is an area found in Snowdin Forest, south of the icy X's and O's puzzle. It is surrounded by glowing mushrooms, and interactable snowflakes (possibly fairies). Glyde is found in this area. The door bears the emblem also found in multiple areas of the game, such as the Turtle Vendor or New Home. To open the door, you must avoid all the credits in the True Pacifist ending. Inside, you find the Annoying Dog, representing Toby Fox, with a computer and some dog residue.