If you are defeated by papyrus instead of seeing a game over screen papyrus will capture you and lock you in the guest room.
Undertale the locked door in.
That key will open the back door.
The door which bears the delta rune is surrounded by glowing mushrooms and floating particles.
Save before talking to sans at the end then reload.
Anyone that s started up undertale for the first time will encounter a mysterious locked door early in the game s snowdin area.
There is no other way to enter this building.
Don t worry though he gives you a nice bed and some food.
The mysterious door is an area found in snowdin forest south of the right side of the room with the icy x s and o s puzzle.
Undertale by indie developer toby fox is a video game for pc ps4 vita and switch.
Finally i got around to doing this.
Glyde can be encountered in this room before fighting papyrus.
Undertale is about a child who falls into an underworld filled with monsters.
In the nintendo switch version examining the door leading to mad mew mew in the dog shrine before it is unlocked yields a message saying that the door is locked by a mysterious seal as an ominous piano jingle is heard.
By the way there s two other keys that you might want to check out if you already haven t.
First you have to get the key to sans room.
Then snoop around there to find an another key that unlocks a hidden door behind the house.
To open this door you must dodge every name during the special thanks portion of the credits after a pacifist run.
To do that you have to save just before he judges you and then reload several times until he gives you the key.
After that you go into sans room and will find another key on a box.
Repeat a few times to get a key to his room.
Come join the fun.