How do I open the door southwest of Snowdin?

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I've tried a variety of things, including checking the door with every possible combination of lit mushrooms, but none worked. The only thing that happened here was a random encounter with (IIRC) Glaze, who killed me very quickly. I never managed to get a rematch, however.
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How do you open the secret door in Snowdin?
If you dodge all the "Special Thanks" credits during the Pacifist ending, the secret door in Snowdin Forest opens up. In the Version 1.001 update, there's a small bit of extra dialogue for choosing to "Fight" the Annoying Dog.How do you open the mushroom door in Snowdin?
To open the door, the protagonist must dodge all the names of the Undertale Kickstarter backers in the True Pacifist Ending Credits.How do you get to the dog room in Undertale?
The Dog Shrine is located in a secret compartment in Snowdin Town. After beating Papyrus and befriending him, return to his home and go on a date. Once inside the house, inspect the really tall kitchen sink, where an annoying dog will jump out of. If you enter the open doorway, you will enter the Dog Shrine.Undertale - Bonus: Snowdin's Mysterious Door
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Images: Harrison Haines, Pixabay, Adrienn, Erkan Utu