AppearanceIn contrast to the bright, sterile color scheme of the Lab, the True Lab is grimy, dark, and fog-filled.
It has a dark green celeste color scheme and an unsettling atmosphere. Assorted objects fill the area, including beds, sinks, refrigerators, wall fans, mirrors, and Golden Flowers. There is a vending machine that dispenses Popato Chisps near the second elevator door.
True Pacifist Route
After the protagonist has completed the date with Alphys by giving her Undyne's letter, Papyrus calls the protagonist and strongly recommends that they meet Alphys at her lab. When the protagonist arrives at the Lab, there is a note in front of the previously locked door, which now opens upon approaching.
After entering the door, the protagonist descends in an elevator that malfunctions and crashes. Once the protagonist enters and activates the elevator, there is no going back to the rest of the Underground and they are locked in the True Lab. They then enter the True Laboratory, where they find several Lab Entries, Amalgamates, and four keys which give access to the power supply to restart the elevator.
In the True Lab, the protagonist learns about how Alphys experimented with Determination, SOULs, fallen monsters, and Golden Flowers. While working with Determination, Alphys resurrected fallen monsters such as Shyren's sister and Snowdrake's Mother, who as a result soon melted into Amalgamates. The protagonist also discovers that Alphys attempted to create a soulless vessel from a Golden Flower; the vessel is heavily implied to be Flowey. Alphys's lab entries provide backstory on her experimentation and are found throughout the True Lab.
While exploring the Lab, the protagonist encounters a strange machine. This machine is the DT Extraction Machine, which Alphys used to extract Determination from the six previously captured human SOULs.
The protagonist also finds several video tapes (all of which have no video aspect to them) that document conversation between Toriel and Asgore, and Asriel and Chara. These tapes imply that Chara possessed darker tendencies and that they attempted suicide as part of a plan to combine their SOUL with Asriel's to pass through the barrier. The VHS TV in this room resembles the TV that projects Photoshop Flowey's face.
The protagonist then restores power to the elevator. Moments later, Amalgamates surround them. Alphys rushes into the room, saves the protagonist, and states that Amalgamates can get violent when not fed. After the Amalgamates leave the room, Alphys thanks the protagonist for the help and mentions that it is not the Amalgamates which would have made her "disappear" but instead something cowardly which she might do. This cowardly act may be suicide considering that some neutral endings tell of Alphys disappearing.
As the protagonist makes their way to the elevator, the exit cuts off, and a voice is heard congratulating the protagonist. The elevator then leaves the protagonist in New Home, with the elevator down to the CORE sealed off with vines so that the protagonist cannot leave. This indicates that the requirements have been met for the True Pacifist Ending.
Genocide and Near-Genocide Neutral Route
Upon defeat, Undyne the Undying informs the protagonist that Alphys has evacuated the majority of the remaining monsters someplace safe, heavily implied to be the True Lab. In the near-genocide ending, Alphys talks for most of the endgame phone call. She says that, despite having to reveal the truth about herself to everyone, people still treat her like a hero.
In the Genocide ending, the evacuation was for nothing; Chara destroys the entire world and ends the timeline.
Lab Entries can be found on the numerous panels can be seen throughout the lab. The entries are numbered from 1 to 21, but there is no 17th entry. Most of the entries contain extensive information about Alphys's experimentation concerning SOULs, Determination, monsters, and Flowey.
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The five VHS tapes can be found in the room with the TV, which is north of the room with the DT Extraction Machine. They contain recordings of Asriel, his family, and the Fallen Child interacting. However, these do not have any visual content.
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- There is a known glitch in which the Blue Key cannot be seen after being dropped, but can still be picked up.
- The teacup mentioned in Entry Number 20 can be found in Alphys's lab, sitting on her desk.
- The DT Extraction Machine also heavily resembles a Cervine (Deer) skull, the same way Sans's Gaster Blasters resemble Canid (Dog) skulls, and Asriel's skull during the final battle resembles a Capra (Goat) skull. Given that Gyftrot's head shares an identical design there may be a connection between them. It also bears some resemblance to one of the heads seen on Photoshop Flowey.
- In the room with the beds, laying down on the bottom left one for a short while will cause an amalgamate to appear and extend out an arm to pull up the cover over the protagonist, then pat their head before disappearing.
- If the protagonist enters the refrigerator room without turning on the ventilation first, the fog will change the protagonist’s interactions with the environment to vague assumptions. The refrigerators will be described as “It’s some sort of cold, rectangular object.” Other observations are:
- “There's something here... It feels like it's breathing.
- “There’s something here... It feels like a tree, ripe with delicious fruit.
- “There's something here... It feels warm, and moist.”
- “There’s something here... Something in the shape of a man.”
- The screens for Entry Numbers 8 and 18 display a red smile instead of green lines like the other entries, possibly because they tell of how Alphys created Flowey, and Flowey disguises his dark intentions with an innocent smile.
- In the game data, there are two 17th lab entries which cannot be accessed in normal gameplay. Alphys's reads "ENTRY NUMBER 17: monsters' physical forms can't handle "determination" like humans' can. with too much determination, our bodies begin to break down. everyone's melted together..." The other is completely in Wingdings and presumed to have been written by W. D. Gaster.
- The walls of the hallway in the True Lab were originally going to laugh at the player. This was removed for being too scary. 
- ↑ Exiled Queen Ending (Undyne left alive) and the Mettaton Ending
- ↑ https://youtu.be/eJI-jppHygI?t=11m50s