A book found in the Snowdin Library
- On the Neutral Route, a series of monster encounters tells the story of Asriel and the first human. On the Genocide Route, the encounters are replaced by Flowey.
- In Asgore's Home, the Heart Locket and the Worn Dagger can be retrieved on the Neutral and True Pacifist Route, and The Locket and the Real Knife can be retrieved on the Genocide Route.
- In the Last Corridor, Sans judges the protagonist based on their EXP and LOVE.
- In the basement, there is a line of coffins labeled with the SOULs of the seven fallen humans.
- The battle against Asgore at the Barrier serves as the final obstacle in the protagonist's journey until Flowey appears and finishes him off.
After Mettaton EX is defeated and Alphys warns the protagonist that Asgore must die for them to be able to pass the barrier, the protagonist enters New Home. A series of encounters occurs, starting in Asgore's Home. These encounters are non-combative (as the monsters do not attack the human), but instead, they detail the well-believed history of Asriel and the first fallen child, about Asgore and Toriel.
It is explained that after the first human had fallen into the Underground, they were found by Asriel and treated as a second child by Asgore and Toriel, but eventually became lethally sick. The human's only wish was to see the Golden Flowers of their hometown. This, however, could not be fulfilled as the monsters were not strong enough to pass the Barrier without a human SOUL. The human died, and in grief, Asriel absorbed their SOUL, passed the barrier, and returned the body of the child to the town.
Believing that Asriel was the cause of the human's death, the townspeople attacked him, and sustaining numerous injuries, he returned with the fallen child's body and consequently perished in the Underground. Heartbroken after losing both of his children, Asgore declared that all humans that fell into the Underground must be killed and have their SOULs collected, so as to be able to destroy the barrier after attaining seven human SOULs. Toriel was disgusted by this, so she relinquished her title of Queen and left Asgore to live in the Ruins in order to protect all humans that fell there.
After this explanation, the protagonist makes it to the Last Corridor, where Sans appears and reveals the meaning of EXP and LOVE. Additionally, he judges the protagonist based on how much EXP and LOVE they have gained. Depending on how many/what monsters the protagonist has killed, Sans's reaction ranges from hesitantly proud to bitter (especially if they killed his brother, Papyrus). If the protagonist gained no EXP, Sans praises the protagonist for not gaining any LOVE. He tells them that they will soon face their greatest challenge, but that he has confidence in them because of their determination to do the right thing. After this, the protagonist confronts Asgore in the Throne Room (A short detour shows a set of seven coffins, of which the closest is titled the name given to the Fallen Human). He is polite, friendly and extremely hesitant during the entire encounter. He goes to wait for the protagonist at the barrier and lets them decide if they have anything to do before their destined battle. Once the protagonist has done everything, they fight Asgore.
After defeating Asgore, the protagonist is unable to go back and must make their way to the exit.
True Pacifist Route
After exploring the True Lab, the protagonist receives a strange phone call and is then forced into New Home, with the elevator to the CORE jammed shut by vines. All SAVE Points except the one in "The End" do not appear, and no monsters (including Sans) are present until confronting Asgore.
When the protagonist confronts Asgore, their friends appear and intervene to stop the fight.
The protagonist encounters Flowey multiple times, starting at Asgore's Home until the Last Corridor, featuring Flowey detailing his thoughts and feelings about his life after being resurrected as a flower with determination, limited positive emotions, and no empathy. Functionally, this is a replacement for the story of Asriel and the human's death given on the Neutral Route.
In the Last Corridor, Sans commences the final boss fight of the Genocide Route. During the battle, he explains that based on the protagonist’s past actions and murders, letting them go would lead to the destruction of the entire timeline. Killing Sans allows the protagonist to enter the Throne Room, which revokes input actions as the ending commences.
New Home is an entirely gray setting, occupied by long corridors and what appears to be a large city in the background. It does, however, contain the Throne Room and the Last Corridor, both of which are well-lit, brightly colored rooms, primarily sunlight-yellow. Onionsan mentions that there is a large aquarium in New Home and that it is overcrowded, but this is never seen.
Castle Elevator to Last Corridor
The initial room is a hallway with a SAVE Point off to the side. The pathway veers upwards into a long, horizontal room with a view of the city in the background. There is an elevator in this room, but it cannot be used until the protagonist reaches the other side. The next room is a vertical room with a few buildings on either side. This room leads to the entrance to Asgore's Home, which is almost identical to the entrance to Toriel's Home, except there is a pile of leaves where the black tree should be.
The layout of Asgore's Home is almost entirely identical to Toriel's Home, right down to the basement up until the room where Toriel is fought. Instead of ending at a door, the pathway veers to the right and continues forward into to a very long horizontal room with another view of the city. The end of this room contains an elevator leading back to the beginning of New Home and a pathway that leads south into the Last Corridor.
Last Corridor to The End
Past the Last Corridor is a vertical hallway that veers to the right, leading to the Throne Entrance. Past the Throne Entrance is a southern pathway that leads to a staircase to the basement. In the basement is a line of coffins labeled with the SOULs of the seven humans that came before the protagonist. Four of the coffins can be viewed in full, while half of the fifth one is cut off. The last two coffins are assumed to be off screen. The only coffin that can be inspected is the one labeled with the SOUL of the first human, which is revealed to be empty. On the True Pacifist Route, the coffins are open, and the first human's coffin is revealed to have mummy wrappings at the bottom.
The Throne Room is a large and open room with birds chirping in the background. Light shines from above, casting an irregular pattern of light and shadow on the floor. In the middle of the room is a throne, assumed to be Asgore's, and cast off to the side is another throne covered by a white sheet, assumed to be Toriel's. The protagonist walks forward on their own, alerting Asgore as he is watering the Golden Flowers that encapsulate the entire room. When Asgore notices the protagonist, the birds stop chirping, and Small Shock plays. When Asgore leaves the room, the protagonist can continue forward into a room that looks similar to the very first room of the game, except without the bed of Golden Flowers.
Asgore leads the protagonist to the Barrier, and from there he reveals seven capsules with six of them containing the SOULs of the six fallen humans and the seventh one being empty. The protagonist fights Asgore, and Flowey finishes him off, absorbing the six human SOULs and transforming into Photoshop Flowey. After Flowey is defeated, the protagonist finds themself beyond the Barrier, in a room that is identical to the rooms where Flowey is encountered in the Ruins.
- In the Genocide Route, the keys are put on the cell phone's keychain, despite the fact that Alphys does not upgrade the protagonist's cell phone with a keychain on this route. This is either an oversight, or an indication that the keychain was an original feature of the phone only mentioned by Alphys in passing.
- "He-hey! That's OK! It beats moving to the city! And living in a crowded aquarium! Like all my friends did! And the aquarium's full, a-anyway, so, even if I wanted to, I..." - Onionsan