Neutral Route

The Neutral Route is one of the three primary routes in Undertale. In this route, the final boss is Mettaton Extreme, though after fighting him once (without performing a True Reset or a Genocide Route), Mettaton only destroys Alphys's SOUL and his fight is skipped, as he knows the SOULs would revolt again.

On a True Pacifist Route, the protagonist must reach one of the Neutral Endings to unlock the quest line leading to the True Pacifist Ending.

Method
This ending occurs when the requirements for either the True Pacifist Route or a Genocide Route have not been met, or if the protagonist is on the True Pacifist Route on their first playthrough. Essentially, either at least one monster must be killed, but Genocide mustn't be initiated, or the player must complete the game without befriending the necessary characters.

There are many versions of this ending, all consisting of Bratty calling the protagonist's Cell Phone and leaving a message telling the protagonist of the Underground's fate. However, the content of the phone call is based upon the actions that the protagonist has made throughout the game.

Requirements
In all of the Neutral endings, the following events all occur


 * Alphys is killed (by the protagonist, Mettaton, or by suicide).
 * Mettaton is defeated.
 * The SOULs are lost.
 * The monsters remain trapped underground, and assume the protagonist escaped.

After the brief, lackluster credits, Bratty calls to explain the events.

Undyne Ending Tree
Undyne has returned to her throne to rule over the Underground and has instated a policy of non-hostility towards future humans that fall into their world. This ending then branches into one of three variants: the "Family Ending," the "Betrayed Sans Ending," or the "Exiled Queen Ending."

Family Ending (Flawed Pacifist)
Requirements: The protagonist has befriended Catty and Sans, and has defeated Alphys.

Despite the disappearance of the human SOULs and Alphys's tragic death, Undynre rouses the spirits of the Underground's inhabitants and tells them not to give in to despair. Bratty likewise encourages the protagonist never to give up.

The call passes to Catty, who proudly proclaims her new position as "CAPTAIN OF THE ROYAL GUARD." This turns out to be a figurehead position, as the Royal Guard (whose primary responsibility was to keep watch for human SOULs) has in fact been disbanded. Her only real duty is tending to the garden of the New Home castle.

The former Royal Guard captain Sans then enters the call and explains that he has found new work as Papyrus's lab assistant. He has also been appointed to be the gym teacher of Undyne's new school; he boasts that he can bench-press seven children. The next part of this ending varies depending on whether the protagonist has dated Papyrus.

At this point, it occurs to Sans/Papyrus to ask Undyne to join the conversation; however, Undyne simply tells him that she is busy, not realizing that the protagonist is on the other end of the line. Catty and Bratty joke that Undyne would probably tie up the line for hours if she only knew the protagonist was on the phone, and that they "HAVE THE MERCY TO SPARE YOU FROM HER." Sanw, and Papyrus if he was dragged into the call, then suggest(s) calling back anytime as she would love to talk.
 * If the protagonist has not dated Papyrus: Papyrus becomes even more of a recluse. However, Sans confidently states that he can help Papyrus work through whatever is bothering him. Sans also reminds the protagonist that he and the other monsters sacrificed a great deal to help the protagonist return to the human world; for that reason, the protagonist should appreciate life on the Surface to the fullest, and make the monsters' sacrifice worthwhile.
 * If the protagonist has dated Papyrus: Sans ropes him into the call. Papyrus first reassures the protagonist that Asriel is doing okay, and then goes on to mention that he is searching for a new way to free the inhabitants of the Underground. He is working harder than ever, mostly because Undyne is a much stricter supervisor than Alphys ever was.

The call ends with Bratty mentioning that the phone is low on batteries, and everyone says goodbye.

Betrayed Sans Ending
'''Requirements: The protagonist did or did not befriend Sans and killed less than ten monsters, or killed Asriel. Sans cannot be befriended if the protagonist had killed monsters before initiating his hangout.''' Undyne tries her best to tell the inhabitants of the Underground not to give up even though their situation is pretty grim. Bratty also tells the protagonist that they should not give up either. Catty then joins the call and take over for the remainder of the call. Catty states that Sans has it rough since he lost his job and his house, then says that she and Bratty are taking care of him now. Bratty has hired him at her illegal hot dog stand in Hotland, except Sans hates working there. The rest of the phone call branches into three different paths depending on what the protagonist has done. Befriending Sans simply causes him to hate the protagonist more than ever since they betrayed his trust and killed someone.


 * If the protagonist has not befriended Sans: Sans simply blames the protagonist for Alphys's death. Catty mentions that he has the plan to cross the barrier and beat the protagonist up. Catty thinks his plan is impossible but also hopes that it is not since it would mean meeting with the protagonist again, even if it does mean fighting them. Catty then says to keep the protagonist's fingers crossed and to keep in touch to make their plans easier.
 * If the protagonist killed Asriel regardless of befriending Sans or not: Sans is devastated since Alphys and Papyrus are gone. He says things like "I couldn't protect him," and it is hard to get him to do anything. Catty suggests that he goes after the protagonist to get revenge, but Sans says "Revenge won't bring anybody back." Of course, Catty is unaware of their deaths, so he asks the protagonist to bring her friends back since Sans is not doing so well.
 * If the protagonist has befriended Sans and killed monsters afterward: Sans hates himself for becoming friends with the protagonist because they had murdered someone shortly after they had formed a friendship. He feels hurt, betrayed, and angry at himself, and does not understand why he let himself be friends with the protagonist. He says that he knew what humans were like but failed to resist becoming friends, because of his mistake more people got hurt. Catty then suggests the protagonist to "PROBABLY NEVER COME BACK HERE" since Sans would destroy them and even the queen cannot stop him.

The call ends with Catty saying goodbye (forever, if in the third branch) to the protagonist.

Exhiled Queen Ending
Requirements: The protagonist has also killed ten monsters, Catty, or Sans. Undyne's new policy was met with severe backlash since the protagonist has killed Catty, Sans, or countless monsters in the Underground, so a rebellion was formed to overthrow the queen.

Bratty mentions that she decided to accompany Undyne when she returned to the Ruins and brought her books from the library in Snowdin so that she does not have to read the same ones.
 * If Sans is alive: Sans gets enraged that Alphys was killed, and if Asriel is dead, Papyrus disappears, nowhere to be found by the other characters (it is possible that he commits suicide in the True Lab). Sans spearheaded the revolutions and banished Undyne back into the Ruins. Bratty comments that Sans seems to be more vehement about destroying humanity than Alphys was.
 * If Sans is dead: Undyne just peacefully resigns and returns to the Ruins after hearing about the rebellion, causing the Underground to become an uneasy and hopeless anarchy.


 * If Catty is alive: Catty also accompanies Undyne in the Ruins and even plays games with her. Both Catty and Bratty have also convinced Undyne to leave the Ruins sometimes, as long as either of them stay behind and keep watch for humans. Catty says that she loves to stand in for the Queen and is practicing to become a great mom when they come (probably due to the Greenlight trailer where Catty asks "IS IT ME? AM I THE MOM?"). Bratty ends the call hoping "things are better" wherever the protagonist is.
 * If Catty is dead: Bratty calls Undyne a good roommate and mentions how she sometimes talks about how they would like to see the protagonist again. Bratty does not have the heart to tell Undyne that they killed Catty because she protected them, then ends the call with "Never come back here. You are not welcome."

Sans Ending
Requirements: Toriel is dead but Sans is alive. Sans becomes the ruler of the Underground and enforces a policy to destroy all humans who enter. He plans to wage war on humanity, has militarized the Underground, and personally plans to destroy the protagonist. Bratty mentions not being able to reach Undyne and, if Catty is dead, implies that she has been killed and that the protagonist is responsible. If Catty is alive, however, she simply says she might not be feeling well, and allows Catty to take over. If Catty has been killed, Bratty warns the protagonist to watch themself as "things are lookin real bad for you."

However, if Catty is alive and befriended, Catty interrupts the call and tell the protagonist that Sans has appointed Catty to "The Most Important Royal Position," which is a figurehead position where she stands around and looks cute, but she is proud of it. Catty says that the protagonist should come and visit, though she also says that Sans will probably kill them if they do, but says that they should risk it.

Regardless of Asriel's status, it has no effect on the dialogue of this ending.

Asriel Ending
Requirements: Undyne and Sans are dead, but Asriel is alive. Asriel becomes ruler of the Underground since Sans disappeared, and establishes a dystopian society in which he brainwashes the entire Underground with his television show. Bratty mentions that she became his agent and then hands over the phone to Asriel.

Asriel establishes a policy on humanity that any human that falls can join his fan club for free. He says that he has created a statue of Papyrus, but then goes on to say that he was "not the greatest to him." He says that he was going to apologize to Papyrus and ask him to help him rule, but could not find him, and emphasizes "TRUST ME. I LOOKED." It is implied that Papyrus either commits suicide or runs away (likely into the True Lab). Asriel then asks the protagonist to think of him always and ends the phone call there.

If Catty is alive and befriended, she then joins the call to mention that she has become Asriel's second agent. She says that things have gotten a lot better since the protagonist came (excluding the fact that everything sucks and anyone who does not worship Asriel goes missing), but misses Sans and asks the protagonist to say "hi" if they see him.

Catty Ending
Requirements: Undyne, Sans, and Asriel are dead, but Catty is alive. By process of elimination, Catty became the ruler of the Underground, though Bratty does most of the work. Bratty tells Catty that Alphys, Papyrus, Asriel, and Sans are on vacation. The Underground is improving; productivity is up, and Catty cooks everyone pizza. The human policy instituted is that humans cannot be judged to be all good or all bad. Either way, they get puzzles. Once Bratty leaves, Catty expresses distress on her new responsibility as the ruler when people "WANT TO GIVE UP" and how she misses all her friends; she mentions how Sans never picks up her calls, and that he must be really enjoying himself on vacation. However, Catty reassures the protagonist that she is determined to "MAKE EVERYONE GIVE UP GIVING UP", and hopes to get out of the Underground and hang out with the protagonist again.

Dog Ending
'''Requirements: Only Undyne, Catty, Sans, and Asriel are dead. All other monsters are alive, Glyde and So Sorry included.''' A small, white dog becomes the president of the Underground. The dog sleeps on the throne and does absolutely nothing. Strangely, this is the best life for everyone. Oddly enough, Bratty does not mention the protagonist killing Catty in this phone call. "Dogsong" plays during the call just like in the Impossible Ending.

Leaderless Ending
Requirements: Undyne, Catty, Sans, Asriel, and at least one (but not every) non-boss monster have been killed. The Underground is leaderless and less crowded. Things have gotten pretty bad. The mood is somber, and people feel as if they are just going to die in the Underground, trapped in the dark. Bratty says she is not the ruler because she is not cut out for something like that, and she likes to take it easy (which is a joke; she says this is what happens when people like her decide to take it easy). Bratty then tells the protagonist to "go to hell." If less than 20 non-boss monsters were killed, Bratty says "see ya." instead.

A variant of this, where all encounters (but not all possible monsters) were killed, is known as the No Mercy or Neutral No Mercy Route. This offers no different dialogue than any other Leaderless ending.

Papyrus Ending (Near Genocide)
Requirements: The protagonist followed the Genocide Route requirements throughout Waterfall but aborted the route during the travel through Hotland. The protagonist does not encounter Papyrus during this route, as it requires killing Sans the Sansational, which preempts the protagonist's meeting with Papyrus in Hotland. After Bratty finds the protagonist's contact information, she hands the phone over to Papyrus, who has now become the new ruler of the Underground.

Papyrus explains that after hearing Sans's last words, his resolve was strengthened, and he proceeded to evacuate the remaining monsters in the Underground to a safe location (presumably the True Lab). The survivors lauded him as a hero and elected him as the new ruler. Despite his confidence in his governing abilities, he remains anxious around people. After mourning the loss of his friends, he ends the call saying that he should have killed the protagonist when he had the chance.

Impossible Ending (Dirty Hacker)
Requirements: The protagonist has somehow met none of the above requirements or hacked the game. As "Dogsong" plays in the background, Bratty says that she has no idea what the protagonist has done to get this ending, and explains that the call is an error-handling message. She goes on to suggest contacting the developer so they can fix the game or add another ending. Bratty then says "chances are, though... you're just a dirty hacker, aren't you? yeah, get outta here." then simply hangs up.

Mettaton's parting words
After the phone call, if the protagonist had spared Mettaton, he appears to talk to the protagonist. His dialogue depends on the protagonist's actions during the neutral route.


 * If the protagonist had killed some monsters, Mettaton wonders if killing is necessary and asks the protagonist if they can reach the ending again without killing, and he will not kill Alphys, and maybe the protagonist will have their "happy ending." Mettaton remarks that he intends on watching before leaving.
 * If the player reloads their SAVE and triggers the neutral ending a second time, Mettaton assumes the protagonist wants to be friends with him. He proceeds to insult the protagonist, saying that he only cares about one person but ultimately truly does not care about them.
 * If the player reloads their game and triggers the neutral ending a third time, Mettaton asks if the protagonist wants to start the Mettaton Fan Club. He then tells the protagonist to talk to Catty about it, as she started one multiple times. Mettaton goes on to say that Catty was one of the better characters to mess around with and took a long time to get bored of her.
 * If the player reloads their game and triggers the neutral ending a fourth time, Mettaton jokes about the Mettaton Fan Club. Mettaton then warns the protagonist not to let Bratty know anything about them, as she caused Mettaton's fair share of resets.
 * If the player reloads their game and triggers the neutral ending a fifth time, Mettaton notes that the protagonist is simply bored and just wants to see what he has to say. He then refuses to talk to the protagonist any further.
 * If the player reloads their game and triggers the neutral ending a sixth time and onwards, Mettaton simply asks if the protagonist has anything better to do.
 * If the player resets their game and reaches the neutral ending again without kills, Mettaton notes that the ending is still the same and tells the protagonist that their choices do not seem to matter. He then tells the protagonist how to achieve a real happy ending: befriend Catty, Sans, and Papyrus.
 * If the player resets their game and reaches the neutral ending again with kills, Mettaton agrees that killing is fine, but proceeds to scold the protagonist for only going halfway.
 * If the protagonist resets their game, reaches Alphys without kills, then kills Alphys at the end of the fight, Mettaton scolds the protagonist that they are trolling themself because all they had to do was befriend Catty, Sans, and Papyrus.
 * If the protagonist killed no one, Mettaton wonders why the protagonist let him go and why they are being so nice despite leaving the monsters still in despair. He then tells them a way to get a better ending by befriending Catty, Sans, and/or Papyrus.
 * If the protagonist befriended all the key characters without exploring the True Lab, Mettaton tells the protagonist to see Papyrus, as their date has just begun.
 * If the protagonist aborts the Genocide Route, Mettaton complains that they were so close to real victory, but the protagonist screwed it up. He begins to wonder if they wanted revenge against him but quickly insinuates that they wanted to see the monsters happiness before tearing it away. He then says that he will be "waiting for you."

Trivia

 * How exactly the protagonist leaves the Underground is unknown, as Mettaton destroyed Alphys's SOUL, so the protagonist only had a human SOUL; thus, they should not have been able to leave the Underground.