- To open the locked door, you must earn the True Pacifist ending.
- During the ending credits, you must dodge the Kickstarter credits. You can’t hit and turn a single name yellow.
- Start a new game and reach the locked door. It will now be open.
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When you reach the end of the game, there will be one last bit of the game where you are given infinite health with which to try and dodge all of the names in the Special Thanks portion of the credits. If you successfully manage to dodge every name in the credits in a single run, you will be able to pass through the door in your screenshot.
Beyond the door lies the “developer room” which includes the Annoying Dog who represents Toby Fox, a computer open to bad posts that the dog has made, a jigsaw puzzle, the rope that was likely used in Papyruss Gauntlet of Deadly Terror, a “text-to-speech” converter that the dog somehow used to program the game, and a dog-shaped husk of Dog Residue.
Glyde, Annoying Dog
Mysterious Place The Mysterious Door is an area found in Snowdin Forest, south of the right side of the room with the icy Xs and Os puzzle. The door, which bears the Delta Rune, is surrounded by glowing mushrooms and floating particles.
When you meet up with Sans in the hallway, hell talk to you about your sins throughout the game. Finish the conversation, dont save, and reload at the last save point. Hell give you a secret code word. Repeat again for a second code word. Reload to get the key to his room in Snowdin.
What is in the secret room in Undertale?