The Artifact Room is a secret location found in Waterfall. It is accessible after solving the Piano Puzzle.
THERE'S SOMETHING ANNOYING ABOUT THIS ROOM. BUT I CAN'T QUITE PLACE MY FINGER ON IT...Papyrus when called in the Artifact Room
The small room is simple in nature and design. The sole purpose of the room is to restrict access to a legendary artifact sitting upon a pedestal. The artifact itself is red and spherical in nature.
Attempting to retrieve the artifact prompts the message, "You're carrying too many dogs", and the Annoying Dog appears in the protagonist's inventory for this room only. When the Annoying Dog is dropped or used, it appears walking from the leftmost visible point from where it is dropped, absorbs the artifact and walks off through the right wall until it cannot be seen, leaving Dog Residue in the protagonist's inventory.
Interacting with the pedestal after the artifact is absorbed brings up text saying "The artifact is gone".
- This room makes a brief appearance in the Steam Greenlight Trailer for Undertale, albeit lacking collision. The protagonist walks through the wall to find Sans, who asks the protagonist if they have noticed the room has no collision. Papyrus shows up from the right and asks if he can be in the trailer, causing Sans to tell him that he is ruining the trailer.
- If the Annoying Dog is removed from the protagonist's inventory through unconventional means, such as opening the Dimensional Box in the debug menu and placing the Annoying Dog there, interacting with the artifact again displays the message: "This will never happen." The artifact sprite remains visible, however, when interacted with again, it shows the general message "The artifact is gone."
- Using the Cell Phone to call Papyrus will bring up dialogue that foreshadows the Annoying Dog.
- According to a call with Undyne, nobody else has ever solved the piano puzzle before the protagonist does. She will then talk about how she has been waiting a long time for someone to solve the puzzle but will then try to play it off. Calling her again brings up dialogue saying that she guesses that she has to find a new mystic artifact.
- Attempting to call Toriel in this room while the Annoying Dog is in the inventory brings up a message stating that "The ringing is coming from inside your inventory." This quote refers to the fact that the Annoying Dog will steal Toriel's cell phone should the protagonist wait in the room where they receive their cell phone. It is implied that the dog stole her phone again and ate it.
- In the Nintendo Switch version of Undertale, a border titled "Super Dog, Hoi" can be unlocked in this room.