True Pacifist Route

The True Pacifist Route leads to one of the Endings of Undertale.

Method
Upon completing the Neutral Route, the protagonist will receive a phone call post credits that will provide a hint to the next requirement in getting the True Pacifist Ending. If Flowey is spared, he will appear afterward and elaborate on the hint, but if he is killed, the game immediately returns to the title screen. The protagonist can then reload their save file to fulfill any missing requirements, as long as they have not gained any EXP/LV; otherwise, they must reset their game. Note that killing Asgore or Flowey does not accrue any EXP, as the protagonist cannot save after fighting them anyway.

The list of requirements are as follows:
 * 1) Throughout the game, never kill any enemies or gain any EXP/LV; essentially, only use non-lethal battle exits (spare, flee, or battle-ending ACTs). FIGHTing monsters or destroying the Dummy in the ruins do not lock players out of this route, as they do not accrue EXP.
 * 2) After fighting Papyrus, visit his house and complete the date/hangout with him.
 * 3) After Undyne passes out from pursuing the protagonist, get a cup of water from the nearby water cooler and pour it on her.
 * 4) Return to Waterfall and go to Undyne's house. Papyrus will be waiting outside. Talk to him to enter the house, then complete the "cooking lesson" and faux battle with Undyne.
 * 5) Complete the Core and spare Mettaton EX.
 * 6) Complete the Neutral Route in order to begin the next series of events.
 * 7) Backtrack out of the Core towards the MTT Resort, to the bridge connecting the two places. There, Undyne will call the protagonist asking to deliver a letter for her.
 * 8) Talk to Undyne outside of Papyrus's house to receive Undyne's Letter upon talking to her.
 * 9) *If the protagonist had reached the bridge without completing the "date" with Undyne, then backtracked to complete such, she will give them the letter at that point, unless their inventory is full in which they will have to receive it from her at Papyrus's house.
 * 10) *If the protagonist discards the letter, they can return to Undyne to receive Undyne's Letter EX, which cannot be discarded.
 * 11) Put the letter under the door of Alphys's Lab and complete the "date" with her.
 * 12) Papyrus will call and tell the player to meet Alphys at her lab. Return to Alphys's Lab to find a note leading to her "bathroom" containing the True Lab.
 * 13) Find the four keys scattered throughout the True Lab and put them in their proper slots to open the generator room. Turn on the generator to trigger a conversation with Alphys. Head back to the elevator near the generator room to be warped to New Home, with the exit vined off. This signals that the Pacifist Ending will occur.

Completing Friendships

 * If you have not befriended Papyrus in a Neutral Pacifist run, proceed to Papyrus's house in Snowdin for your date/hangout with him.


 * If you have not befriended Undyne in a Neutral Pacifist run, proceed to Undyne's house in Waterfall. Papyrus will be waiting there.

Befriending Alphys
At the entrance to the Core, Undyne calls the protagonist (at the behest of Papyrus) to ask them to deliver her letter to Alphys.

If you befriend Undyne after a Neutral Pacifist run, she will give you the letter immediately after befriending her, saying Papyrus suggested it to her earlier, but she still hated you at the time.

After delivering the letter to Alphys, she mistakes the letter as being from the protagonist themself, and goes on a date with them.

During Alphys's date, the two go to the garbage dump near the Waterfall. They bump into Undyne, who decided to deliver the letter herself. Alphys tells Undyne some truths about her 'scientific' work, which was just her lazing around and watching anime and reading manga. Undyne expresses her support for Alphys, sending her off to train with Papyrus. She then confronts the player about anime, asking if it is real.

After the date, Papyrus calls the protagonist and very specifically instructs them to go to Alphys's lab, citing no reason other than a 'good feeling' he claims to have about doing so (This may be because Flowey told him to tell the protagonist, but didn't want the protagonist to know).

True Lab
Arriving at the lab, the player finds a note from Alphys, in which she declares she will 'face [her] own mistakes'. The note tells the reader to enter what was previously thought to be Alphys's bathroom to discover the truth, in case Alphys does not return.

The protagonist enters the door, discovering it to be an elevator. They take the elevator down to the True Lab, but it loses power, leaving them stuck in the lab. Exploring the lab, they find logs from long ago, detailing Alphys's experiments with souls and determination to restore monsters from death. Injecting determination into the dead monsters successfully restored them to life, but they melted and turned into amalgamates - fusions of several monsters. Several of these amalgamates attack the protagonist, but the protagonist spares them. The protagonist sees the determination extractor, resembling part of Flowey's form during his boss battle in the Neutral Route, and they learn that Alphys did some experiments with golden flowers, which produced a single living specimen who escaped.

The protagonist switches the power on, restoring power to the elevators. Alphys appears and saves them from some amalgamates, who she explains were hungry, resulting in their aggression. She further explains that the monsters' bodies couldn't handle the determination and melted together. Alphys thanks the player for their support, and declares to the amalgamates that they will return home.

Alphys leaves the true lab, and the player returns to one of the elevators. They receive a call from someone they do not recognize. The voice, implied to be Asriel, calls the protagonist by the name given to the Fallen Human at the beginning of the game, and tells them that 'everything has fallen into place' and that the voice will 'see you soon'.

The elevator appears to malfunction, and lands the protagonist at the entrance to New Home. Vines jam the elevator shut.

The Barrier
At the barrier, the player confronts Asgore. As they prepare to fight, Toriel arrives, incapacitates Asgore, and consoles the player. After reprimanding Asgore for his actions, even going as far as to give him a simpler way to retrieve human souls, she is shortly later followed by Sans, Papyrus, Undyne, and Alphys who all begin to chat. To Alphys's surprise, Papyrus reveals that a 'tiny flower' helped him call everybody to the Throne Room.

Flowey arrives and traps the other monsters in vines. He then thanks the player for bringing them all to one spot, saying that he absorbed the humans' souls while the protagonist's friends were chatting, claiming he will absorb them all as well to achieve his 'real form'. He then reveals his true motive for causing the player so much trouble - to keep them playing the 'game' so that they can 'play' with him forever. He gives the player a chance to face him, promising to return everyone's souls and break the barrier if they win. As if to deny them even this, he plans to keep them trapped before mercilessly attacking them, saying he is willing to "kill them 1,000,000 times" to prove his point. Before delivering the final blow, the player's friends protect them from Flowey's attacks while both healing them and encouraging them to win. Shortly afterwords, many of the monsters that the player spared through out the game arrive, healing the player and seemingly putting Flowey off guard. However, he suddenly laughs at them for their 'stupidity' and absorbs their souls.

The player sees that Flowey is now a young monster in a striped shirt similar in appearance to Toriel and Asgore. He calls the player by the Fallen Human's name, then transforms into an older, more powerful looking monster, introducing himself as Asriel Dreemurr. Asriel attacks the player's soul; if the player's HP reaches 0 and their soul breaks, instead of restarting the game, the message "But it refused" appears and the soul reforms through determination and fully restores its health. After this happens once, the soul will simply reform and return to the battle.

Asriel changes into an even more powerful form, threatening to reset the world's timeline, restraining the protagonist and preventing them from doing anything except struggling. The protagonist realizes that while they can't save their game, they can save the monsters' souls. They reach out to their friends' souls (which are trapped in Asriel's soul) and bring them back by restoring their memories. After saving all their friends, they begin to save Asriel himself and see memories of him befriending the first human. The protagonist's friends' souls resonate within Asriel; he begins to cry and his fire attacks start avoiding the player's soul. He then begs the player to let him win and attacks them with his strongest attack. The protagonist survives with their HP reduced to an extremely small decimal value and saves Asriel, returning him to his form as a child.

Asriel apologizes to the protagonist. He tells them that the first human has been gone for a long time, and asks them for their real name, which is revealed to be "Frisk". Asriel tells Frisk that the monsters' souls allowed him to feel their emotions and desires - their love for Frisk and their desire for freedom, respectively. He expects Frisk to not forgive him for everything that happened, but the player can choose to anyway, surprising Asriel. Using the six humans' souls and the monsters' souls along with their determination, he destroys the barrier.

Asriel returns the souls, and tells Frisk that without everyone's souls, he will eventually return to being a flower. He asks them to forget about him and leaves, but Frisk has the option to console Asriel, causing Frisk to approach and hug him.

Reunited
Frisk wakes up in the room behind the Throne Room, much to the relief of their friends, who all know Frisk's name but they do not remember much about what just happened. Toriel encourages Frisk to do as they wish, whether that be heading for the surface or going for a walk Underground to see the rest of their friends. The monsters inform Frisk that they will follow them to the surface when they're ready.

If the player takes Frisk to the beginning area of the game where the golden flowers broke their fall, they will find Asriel there tending to the flowers. Asriel will be only there if the player hasn't left the Underground before on the current play-through.

The End
Leaving for the surface will end the game.

Frisk and their friends watch the sunset on the surface. Thinking about the future, Asgore asks Frisk if they would act as the monsters' ambassador to the humans.

Papyrus leaves to make a good first impression on the humans, having declared himself the mascot or ambassador depending on the player's decision. Sans, Undyne, Alphys and Asgore leave to help Papyrus.

With everybody else gone, Toriel asks Frisk what they will do now. The player is prompted to choose if Frisk wants to stay with Toriel or not. The player's decision determines the post credits scene.

During the credits, the player gains control of their soul during the special thanks, which are dedicated to the game's Kickstarter backers, and are challenged with dodging the backers' names. If they haven't touched a single name, then the Mysterious Door in Snowdin Forest will open.

After the credits, if Frisk is staying with Toriel, another scene will play, showing them in their new home on the surface. If Frisk parted ways with the monsters, then a photo of Frisk and their monster friends is shown. The Annoying Dog appears after some time at the ending screen. The player can do nothing except quit the game.

If the player reopens the game, Flowey speaks to the player, telling them that 'there's nothing left to worry about'. He points out that the player is the only threat left, as they have the power to reset everything. He then asks them not to reset the game, which would return everybody to when they were trapped underground, and asks the player to let them go. Flowey then asks that if they still wish to reset the game, the player needs to erase Flowey's own memories as well. Believing they might have heard this a hundred times already, he says his goodbyes to the player, calling them by the name given to the First Human at the beginning of the game.

The game's menu has none of Frisk's friends, as they have all left. The menu music is a significantly slowed down version, giving an ominous tone. The player can load their save, which takes place before the ending, and they can replay the credits (and the special thanks) from there (though Asriel will not appear). The menu's reset option is replaced with 'True Reset'; this allows the player to rename the Fallen Human. Choosing a name resets the game and removes everybody's (including Frisk's and Flowey's) memories.

Trivia

 * It is only in the Pacifist Route that the player learns the protagonist's name, Frisk.
 * Examining the mirror in Toriel's home after the final battle gives the description: "Still just you, Frisk."
 * Naming the fallen human "Frisk" at the beginning of the game will activate Hard Mode.


 * After saving Asriel, the player can go to Sans' back room and find a photo of "[Frisk] standing with Sans and all your friends". This photo is implied to be the one the player sees if they decide not to stay with Toriel.
 * There is a glitch where the player can fight and kill enemies in the Core before receiving Undyne's Letter. This glitch allows the player to reach the ending even after gaining EXP and LOVE.
 * After beating Asriel but before seeing the credits, if the player backtracks all the way to the flower patch at the very beginning of the game, they can see Asriel tending to them and have one last talk. Once you view the credits, Asriel vanishes and will not appear there anymore.
 * If you press the spacebar, when Alphys and Undyne are standing close to each other, after the Faux Asgore battle, then it will start their kissing animation very early.
 * The monsters that appear before Flowey turns into Asriel are: Monster Kid, Vulkin, Shyren, Snowdrake, Muffet, RG01, Froggit, and Greater Dog. This is the only time a Froggit is seen outside the Ruins, as one of the Froggits in the ruins, after the True Pacifist ending, imply that they were unable to leave before Toriel left.