Gaster follower
Well, I needn't gossip.
After all, it's rude to talk about someone who's listening.Gaster follower 3
The Gaster followers[note 1] are a trio of hidden characters in Undertale. They are found in certain areas in Hotland and only appear at specific fun values. They appear to have some connection to W.D. Gaster, the royal scientist preceding Alphys.
The Gaster followers are entirely grayscale. Two of them resemble existing characters, and the third one is completely original, but resembles a Deltarune character.
Gaster follower 1[note 2] bears a resemblance to the ficus licker. They have a round face which consists of an emotionless expression accompanied with large eyes. Their arms are small compared to the rest of their body. A double cross marking is present on their chest.

Gaster follower 2[note 3] bears a resemblance to the scared donut guy. Their face is entirely shadowed with a visible mouth but no visible eyes. Their right hand is clutching the side of their head, and their left arm is extended downwards, holding a talking head. The follower speaks through the head in their hand.
Gaster follower 3[note 4] bears no resemblance to any existing character in Undertale, although they do bear resemblance to the Striped Bird from Deltarune. They resemble a large face sprouting out of the ground. A single large eye is present at the top.
The Gaster followers each bear knowledge of Gaster that is not displayed in any other character. They appear to show some admiration for Gaster.

The Gaster Followers appear near the elevators in Hotland. Only one Gaster follower can appear in a single playthrough of Undertale, and they disappear after talking to them. They do not appear on the Genocide Route or during the epilogue of the True Pacifist Route. If the protagonist attempts to call Papyrus (or Papyrus and Undyne) using the Cell Phone while in a room with a follower, they only get the line "The phone won't turn on." The protagonist can still attempt to reach Toriel over the phone. The phone works normally after leaving the room.
Gaster follower 1 has a 50% chance[1] to appear if the fun value is 62. They are located outside of elevator L3 and claim that Gaster's life was cut short after falling into his creation.[2] They later wonder if Alphys will end up the same way as Gaster. This follower disappears once the protagonist leaves the room.
Gaster follower 2 has a 20% chance[3] to appear if the fun value is 61. They are located outside of elevator R1 and claim that Gaster disappeared without a trace, shattering across time and space. They then claim to be holding a piece of him before suddenly vanishing.[4] The sound effect played when they vanish, snd_mysterygo, is the same sound effect that plays when the mystery man vanishes in room_mysteryman.
Gaster follower 3 has a 50% chance[5] to appear if the fun value is 63. They are located outside elevator L2 and claim that Gaster's life was cut short after an experiment went wrong.[6] They then stop and mention that they should not gossip about someone who is listening.[7] They disappear once the protagonist leaves the room.
A character resembling Gaster follower 3 makes an appearance in Deltarune. They are fully colored and take the appearance of a striped bird monster.
- ↑ gml_Object_obj_gaster_follower_b_Create_0 script, lines 35–45
- ↑
It makes sense why ASGORE took so long to hire a new Royal Scientist.
— Gaster follower 1
After all, the old one... Dr. Gaster. What an act to follow!
They say he created the CORE.
However, his life... Was cut short.
One day, he fell into his creation, and... - ↑ gml_Object_obj_gaster_follower_a_Create_0 script, lines 35–43
- ↑
Alphys might work faster. But the old Royal Scientist, Doctor W.D. Gaster?
— Gaster follower 2
One day, he vanished without a trace.
They say he shattered across time and space.
Ha ha... How can I say so without fear?
I'm holding a piece of him right here. - ↑ gml_Object_obj_gaster_follower_c_Create_0 script, lines 35–45
- ↑
I understand why ASGORE waited so long to hire a new Royal Scientist.
— Gaster follower 3
The previous one... Dr. Gaster.
His brilliance was irreplaceable.
However, his life... Was cut short.
One day, his experiments went wrong, and... - ↑
Well, I needn't gossip.
— Gaster follower 3
After all, it's rude to talk about someone who's listening.