If the mystery key is used on the mysterious door it reads the following text.
Undertale locked door.
First you have to get the key to sans room.
Cinnamon bun reward.
The protagonist can sleep in this room for 200 g yielding a similar effect to resting at snowed inn.
Anyone that s started up undertale for the first time will encounter a mysterious locked door early in the game s snowdin area.
Handing over any of the listed items rewards a response and in most cases an item.
You used the key the lock clicks.
As the key failed to fit in the hole.
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.
Glyde can be encountered in this room before fighting papyrus.
You used the mystery key.
To do that you have to save just before he judges you and then reload several times until he gives you the key.
The door which bears the delta rune is surrounded by glowing mushrooms and floating particles.
Sea tea reward.
Nothing belongs to me.
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.
Frisk do not let them in.
There is a dog behind this door.
Nothing will open it not even the expensive mystery key item.
That key will open the back door.