The NPC disappears once the player leaves the room.

It is an exclusive NPC of the version of Undertale for Nintendo Switch, it appears only at the end of the true pacifist route, at the end of its dialogue it disappears with the same sound effect with which Mystery Man disappears, which may mean a possible relationship with Gaster.

It is presumed that Sans could have a connection with W.D. Gaster due to his taste for science, and for the weapons he uses on the Genocide Route.

In the laboratory of sans Room 80 (room_tundra_sansbasement) it is possible for the player to read the plans at the top of the table, which are said to be written in symbols or “handwriting” that could connect with windings, which at turn could connect with WD Gaster. The broken machine there, according to Toby Fox, cannot be repaired. Which means that if this was Gaster’s creation he fell into, then Gaster is destined to remain obliterated.

Additionally, Sans uses a burst weapon (“blaster” in English) during their fight in the Genocide Route called “gasterblaster” (rough translation “arrazadoragaster” or “blastgaster”) indicating that they are a device made by Gaster. An alternative interpretation could be that they are weapons specially made to be used against Gaster.

Editing the room number in the save0 (“saved0”) and .ini file to Room 264 (“Room 264”) (room_gaster) will bring up a message that reads the following:

The “two” he mentions, it is speculated that they are Sans and Papyrus (it is theorized that Gaster has some relationship with Sans, but Papyrus could be replaced with another character), Toriel and Asgore (being the real scientist, Gaster was in the service of kings, but unlikely) or Sans and Alphys (since these are the only characters with a scientific basis). The font used, Wingdings, contains hand symbols which may be a nod to “The man who speaks in hands” which is mentioned by the Person of the River.

The audio heard during input is titled “mus_smile” in the game files. This file can be sped up significantly to reveal Muffet’s laugh, reversed, and repeated. However, it is unlikely that Muffet has any connection to Gaster, as Toby Fox generally re-uses this laugh frequently during play with other classes of enemies.

Community content is available under CC-BY-SA unless otherwise noted.