Mettaton

Mettaton is a robot with a SOUL and was built by Alphys. Initially poised as an entertainment robot turned human killing robot, Mettaton is later revealed to have only acted as such so that Alphys could rescue the protagonist, feel important and become closer to them. Mettaton is the sole television star of the Underground.

Initial Form
Mettaton originally appears as a gray, largely rectangular box with a grid of lights at the top, similar to the mechanism in Snowdin Forest used for Papyrus's Tile Puzzle. The grid of lights can change colors, and Mettaton uses these color changes in place of facial expressions. He has four dials along the bottom of his body, and the bottom, he has a single leg which ends in a wheel. He has two segmented robotic arms which end in white gloves.

Mettaton EX
After having the switch on his back flipped in a Neutral or True Pacifist Route, Mettaton transforms into Mettaton EX; a new body he specially requested Alphys make for him. In this humanoid form, he has black hair with a long fringe that seems to cover his right eye, pale "skin" and visible metal segments below and above his left eye.

He has a pink chest piece, a narrow metallic waist with a box contraption, and black shoulder guards above his segmented arms, which end in gloves. The chest piece has what appear to be a speaker and some knob or gauge, while the waist has two parts that seem to act as a locking mechanism that holds his "heart-shaped core," as they both lose white pixels during his "heart-to-heart" attack. His long black-clad legs end in pink high-heeled boots.

Mettaton NEO
After being confronted by the protagonist on the Genocide Route, Mettaton transforms into Mettaton NEO, which resembles Mettaton EX, but has a more combat-oriented design.

His right forearm is replaced by what appears to be a cannon, pauldrons clad his shoulders, which are shaped like legs and are longer than his arms, and he has wings on his back. The soul on his waist points upwards in a more monster-like manner, and he has a heart shape engraved on his chest plate like Undyne the Undying. His hair on the right side is spiked out, revealing an entirely black segment of his face, with a sparkle or crosshair in place of his right eye.

Personality
Mettaton is a confident, charismatic, and charming TV host that loves drama, action, and violence. He lives for his ratings and adores performing. He supposedly strikes a pose when he does something wrong and makes time on his various shows to beat up "heel-turning villains." He shows a rather shallow appreciation for existence at times. However, despite his seemingly narcissistic personality, he deeply cares about the seemingly positive impact his show has had on the inhabitants of the Underground.

Neutral Route
When meeting Alphys in the Lab, the protagonist is warned about a machine that she had created, Mettaton. Alphys describes it as a robot that was made to be a TV star but eventually had anti-human combat features added (presumably as a way of getting attention from Asgore).

Immediately after this warning, Mettaton bursts through the wall (noted to be only a few feet wide, indicating that he was lying in wait for the protagonist for some time) and forces the protagonist into a deadly quiz show.

Quiz Show
Mettaton asks a series of multiple-choice questions that must be answered correctly within several seconds (the number says 30, but goes down approximately two numbers per second, giving only 15 seconds to answer). If incorrectly answered or not answered within the time limit, Mettaton fires an unavoidable electric shock that halves the protagonist's health. In spite of this, it is impossible to die during this quiz show. Alphys on the top right gives answers via hand motion; realizing this, Mettaton chooses to humiliate her by quizzing the protagonist on the identity of her unrequited love interest. Regardless of the protagonist's choice, Mettaton ultimately departs, concluding that the quiz show has lost all dramatic tension.

Cooking with a Killer Robot
As the protagonist journeys through Hotland, Mettaton entraps them in deadly pastiches of various media genres. First, he forces the protagonist to become his assistant in a cooking show where Mettaton is preparing a cake with a human SOUL as the main ingredient, and he attempts to kill the protagonist with a chainsaw to attain it. Alphys calls in as an interruption and suggests that some viewers may be vegan in an attempt to stop Mettaton from harvesting the protagonist's SOUL as an ingredient, so instead, Mettaton points towards a human SOUL-flavored substitute on top of a faraway cupboard.

However, the cupboard begins to shoot up from the ground rapidly, forcing the protagonist to use the jetpack feature previously installed on their phone by Alphys. They fly to the top and retrieve the substitute within a time limit set by Mettaton while he drops eggs, flour, and milk, all of which slow the protagonist's ascent. Either way, he comments that he was foiled yet again by Alphys. Upon interacting with the substitute after this encounter, it shows the can was stuck to the table, so the protagonist would not have been able to get the substitute given the chance.
 * If the protagonist reaches the substitute within the time limit, Mettaton states, like all cooking shows, he had already baked the cake ahead of time before leaving.
 * If they fail, Mettaton suddenly claims the show is on commercial break and refuses to kill them as there are currently no viewers.

MTT News
Secondly comes a breaking news segment, in which Mettaton asks the protagonist to report on one of the several items within a room ( a dog, a video game, a movie script, a basketball, a present, and a seemingly normal glass of water), which all turn out to be bombs hidden by Mettaton. Mettaton then scatters the bombs around the area, and the protagonist is forced to find and defuse all of them with one of Alphys's phone installments before a larger bomb in the center of the room goes off.
 * If the protagonist defuses all the bombs in time, Mettaton declares that the bomb now explodes in two seconds instead of two minutes.
 * If the protagonist has not disabled all the bombs until ten seconds before the big bomb explodes, the time slows substantially.
 * If the protagonist has not disabled all the bombs before time expires, Mettaton states that the protagonist failed to disarm them all within three minutes. However, even factoring in the slower passage of time through the last ten "seconds" of play, the total amount of time given to defuse the bombs still amounts to under three minutes.

Regardless of whether the bombs were defused or not, Alphys hacks the big bomb and disables it.

During the news segment, a ticker at the bottom of the screen reports the following news.

UNDERTALE the Musical
Thirdly and finally, Mettaton traps the protagonist within a musical, where Mettaton sings about a forbidden love between him, a monster; and the protagonist, a human. He mentions how sad it is that they must be sent to the dungeon, before opening a trapdoor underneath them into a room with a colored tile puzzle. Mettaton announces that the protagonist must pass the colored tile puzzle within a set time before a line of flame comes at them from the side and burns them to death. Mettaton proceeds to engage the protagonist in battle after the tile puzzle. However, Alphys has one final installment on the phone she had given to the protagonist. This yellow button fires a projectile at Mettaton, which the protagonist can use in succession. Mettaton acts like he is defeated from such projectile and flees. If the protagonist does not activate yellow mode, Mettaton attacks with boxes until the protagonist has barely any health left.
 * If the protagonist manages to complete the puzzle, Mettaton deactivates the flames "knowing" that Alphys would have done so.
 * If the protagonist fails, the flames draw near, only for Alphys to disable them.
 * If the protagonist has stepped on a green tile, Mettaton reminds them that the tile signals a monster, which turns out to be Mettaton himself.
 * If the protagonist has not stepped on a green tile, Mettaton repeatedly says "well" before acknowledging that the protagonist never stepped on a green tile, but still fights them.

End of CORE Encounter
After the protagonist reaches the end of the CORE, they are once more confronted by Mettaton. This time, however, Mettaton reveals that he had re-arranged the CORE and hired monsters so as to attempt to kill the protagonist legitimately. He states that Alphys had set up an extensive plan to self-insert herself into the story because she liked the protagonist so much and wanted to feel important by helping them. All of the previous threats from Mettaton were entirely fake, and everything was acted out, and used by Alphys to ally herself further with the protagonist; Alphys plans to intervene in the fight between Mettaton and the protagonist by "deactivating" Mettaton and thus appearing heroic to them. This time, however, Mettaton has made plans to prevent Alphys's aid, so that he could have an actual battle against the protagonist, and locks the door to prevent Alphys from entering. He explains that he wants to take their SOUL so that he can leave the Underground and become a superstar on the Surface. This way, Asgore cannot destroy the Barrier and re-ignite the war between humans and monsters, which would take a toll on his views.

Mettaton EX
Mettaton attacks the protagonist, but under the advice of Alphys, the protagonist tricks Mettaton into turning around so that they can flip the switch on his back to make him vulnerable. This switch transforms Mettaton into Mettaton EX and begins the true game show. By taking damage, using popular brand items, or using specific ACTs to raise the Ratings of the show to above 10 000 (or 12 000, if he still has legs), Mettaton stops the battle.

To his surprise, this is the highest rated episode he has ever had and begins to take call-ins from viewers. Several callers, the first of which is Napstablook, convince Mettaton that he is highly valued in the Underground, and is the primary (perhaps only) source of entertainment that many of the inhabitants have. He is moved by their passion for the show and decides that he no longer wishes to leave the Underground, as well as explaining that the protagonist is strong enough to defeat Asgore. He then deactivates, limbless – whether his limbs fell off during the battle or not – as he runs out of battery power; his body can later be found in the Lab where he is undergoing repairs.

If Mettaton EX is killed, he reverts to his old Mettaton form in the world, though visibly severely damaged. Examining the corpse warrants the description "It's completely trashed."

Mystery Key
If the protagonist purchases the Mystery Key from Bratty and Catty, they can enter the house to the right of Napstablook's. The room is primarily pink, with a bed, a star patterned pillow, star-patterned wallpaper, a pink TV, a window, and a star imprinted rug. Through a series of diaries, the house is shown to be owned by another ghost known as "Napstablook's cousin" within the game (though Papyrus states that his headcanon name for him was "Happstablook"). After meeting Alphys, she designed a body for Mettaton to inhabit.

Using the Mystery key during Mettaton EX's fight prompts him to pretend "it isn't there."

True Pacifist Route
In the True Lab, there is a log entry stating that Alphys fears that Mettaton may not talk to her anymore after receiving his new body.

At the end of the game, when all of the Monsters encountered as bosses have united before Flowey intervenes, Mettaton EX shows his leg from the right side of the screen. He tells Alphys and Undyne that they should kiss already since the entire crowd wants it.

After defeating Asriel, if the protagonist returns to Waterfall before exiting New Home, Mettaton is seen standing outside Napstablook's cousin's house, having recruited Napstablook as his sound mixer and Shyren as his backup singer. During the credits, he is shown on tour, able to use his original box form in conjunction with his new body's legs.

Genocide Route
Mettaton shows up once the protagonist reaches Alphys's Lab and then tell them that he will not battle them, knowing that he is no match for them. He shows up at the CORE and realizes that the protagonist means not only to kill monsters but all of humanity as well. Claiming his main human eradication functions were never fully removed, he transforms to Mettaton NEO. Despite all the buildup, he has no attacks, and the protagonist can destroy him in a single attack. Killing him sets the protagonist's EXP to 50 000, resulting in their LOVE reaching 19.

Contrary to popular belief, missing or inflicting low damage on Mettaton NEO does not fail a Genocide Route. Any attack deals between 900 000 and 999 999 damage, and a MISS simply causes the game to return to the battle screen.

The only way for Mettaton NEO to say that the protagonist was "holding back" is by failing to depopulate Hotland. Mettaton points out the protagonist's lack of killing intent, telling them that they are not "absolutely evil" before dying. This event aborts the Genocide Route and leads to either the Leaderless or Alphys Ending of the Neutral Route.

Frisk
Initially, Mettaton actively antagonized the protagonist under the assumption its original purpose as a human eradication robot along with directive errors gave it an intensified hate for humans and a need to murder them. This was proven to be an act, however, as Mettaton mentions loving humanity, but continued to go against the protagonist on his terms to take their SOUL and prevent a possible war by Asgore. After their battle, however, he was confident the protagonist was strong enough to avoid this themselves.

Alphys
Mettaton initially bonded over their common interest in the culture of humanity, and he is grateful of Alphys for making his physical body. Soon after he receives his initial body, he often belittles her and her interests. However, he owed Alphys enough to play along with her plan to act out the role of a genocidal robot before eventually going on his agenda with the protagonist. Despite this, in the ending where he is given the role as king, he mentions how he regrets being cruel to her before she went missing.

Napstablook
Before he got his body, he was Napstablook's cousin, helping them with the snail farm and living next-door to them. They seemed very close, to the point that Mettaton originally declared that he would never leave them behind and often called them Blooky (a trait he kept). Although he had since left them for stardom, he obviously cared for his cousin, looked regretful when Napstablook called into the program to give gratitude for his show ever since he left. Once he had his permanent new body, he immediately recruited his cousin on his tour so they could stay together.

Trivia

 * If "Metta", "Mett" (case insensitive) or "MTT" is typed for the fallen child's name, the response becomes "OOOOH!!! ARE YOU PROMOTING MY BRAND?".
 * The name "Mettaton" can be interpreted and decoded into various different forms:
 * "Mettaton" is similar in pronunciation and spelling to "Metatron," the highest angel in Jewish lore, also known as the Voice of God and Recording Angel, whose name is transliterated into Greek as MTT. This could be a reference to Shin Megami Tensei's Metatron specifically, as both have metallic appearances, have similar poses, and are very powerful late-game bosses.
 * The name could also be a combination of "metal" and "automaton."
 * It could also be referring to the prefix meta-, which means to change, possibly referencing Mettaton's different forms.
 * "Mettaton" may be a portmanteau of "Meta" and "ton," as Mettaton offers many instances of meta-commentary on the structure of Undertale. Examples include referencing the viewer if one picks "Don't Know" for Alphys' crush question during the quiz show, his words turning into bombs in the news report, changing the window name during his musical segment, mentioning room numbers before his colored tile maze, discussing Toriel plushies in the epilogue and offering a newscast to the fourth wall while the protagonist is visible on-screen.
 * Mettaton's designs show similarities to Undyne's forms.
 * Mettaton EX has shoulder pads similar to Undyne's, both of which are longer and spikier in the Genocide Route.
 * Both have one of their eyes covered in the Neutral and True Pacifist Routes (Undyne with her left eye covered, and Mettaton with his right). In the Genocide Route, these are revealed, showing Mettaton NEO's sparkling/crosshair eye and Undyne the Undying's empty socket that frequently emits a spear-shaped flash of light.
 * Undyne holds a spear in her right hand, and Mettaton NEO has an arm cannon replacing his right hand.
 * Mettaton's design is also similar to other characters not belonging to Undertale.
 * Mettaton EX's design bears a striking resemblance to the outfit sported by Ziggy Stardust; alter ego of English songwriter and pop culture icon, David Bowie. The overall design of Ziggy's attire greatly influenced the design for Mettaton EX while David's eccentric personality and demeanor (from his crossdressing to his philosophies and fans) influenced Mettaton's design as a character.
 * An early concept art design for Mettaton EX bears a striking resemblance to Shadow DIO from JoJo's Bizarre Adventure.
 * Mettaton's normal form resembles the coin-operated robot Cooker from the Wallace and Gromit short "A Grand Day Out," as confirmed by the artbook.
 * Mettaton's normal form also has a similar shape to an NES Cartridge.
 * Mettaton NEO resembles Bass's "Treble Boost" form from the Mega Man series.
 * Mettaton is at least partially inspired by Twitter user nerdbotmk2.
 * Mettaton EX's attitude is very similar to Maximillion Galactica's, a character from Ace Attorney: Justice For All. Along with this, his EX's physical appearance resembles Matt Engarde, another character from the same game, very closely. Both have a similar shirt (in MTT's case, torso) and the hair over the right eye.
 * Mettaton EX's facial features and his personality also greatly resemble those of Harvey Moiseiwitsch Volodarskii from the game No More Heroes.
 * In his box form, Mettaton's overworld sprite has five squares under the main screen, while his battle sprite only has 4.
 * Along with Flowey, Mettaton is one of the only characters in the game to have a voice clip, exclaiming "Oh, yes!" when he transforms into Mettaton EX, and "Yeah!" when attacked in his Mettaton EX form.
 * Stepping on a green tile during Mettaton's Multicolor Tile Puzzle plays the same "Yeah" as the one played when attacking Mettaton EX.
 * In MTT News, the game where Mettaton states he appears 3/4 into may be Undertale, since he does appear 3/4 into the game and it uses the same sprite as the game behind Mysterious Door that was programmed by the dog (presumably Toby Fox).
 * Several unused sprites for Mettaton EX's head show his right eye, and what appears to be the machinery on his face.
 * The answer choices to the question What are robots made out of? in his quiz show have several references.
 * "Hopes&Dreams" references the track "Hopes and Dreams," among other recurring mentions of this phrase.
 * "Snips&Snails" and "Sugar&Spice" are references to the nursery rhyme "What Are Little Boys Made Of?"
 * Mettaton, at the beginning of the MTT News segment, states that "an interesting situation has arisen in eastern Hotland." The MTT News room is solidly located in central Hotland and is considerably farther west than other Hotland landmarks, given the length to which Hotland's third floor and the CORE extend east.
 * When interacting with the video game in the newsroom – which is heavily implied to represent Undertale, given its graphical similarities to the Undertale box cover, as well as the following – Mettaton states that his appearance doesn't occur until three-fourths of the way through the game, which typically over-estimates an average player's progress through the game. Mettaton even states that the game is one where the player should check everything twice if checked twice, referencing the dialogue changing in the game if something is checked or spoken to twice.
 * Mettaton's box form is identical to the console that operates the colored tile maze in Snowdin Forest, and this machine may have been Mettaton himself; during his colored tile maze, Mettaton remarks that the protagonist has seen the puzzle "ABOUT A HUNDRED ROOMS AGO" and presumes that they remember the rules.
 * During Mettaton's singing performance to the protagonist, the program window is renamed to "UNDERTALE the Musical."
 * The song and the scenario from the musical are a reference to the "Maria and Draco" opera from Final Fantasy VI.
 * Mettaton EX recognizes answers for "sexy," "foxy," and "tantalizing" in his essay question, but since the X and Z keys cannot be inputted without holding CTRL, they are only possible inputs in the PlayStation versions.
 * Mettaton EX originally saved images of all the essays to the computer's hard drive. This feature was removed for being too buggy.
 * According to the Undertale Kickstarter, there were originally plans for the protagonist to have a robot husband, which is presumed to be Mettaton. This feature ended up being cut out of the final version of the game for unknown reasons.
 * Additional evidence that points to this event is an unused variation of the Start Menu that can be found in the game's files and explains why the full menu suddenly includes Mettaton and Napstablook.
 * In Undertale v1.001, Mettaton's stats for his box form have been changed from "10 ATK 999 DEF" to "ATK 30 DEF 255." 255 is the maximum value of an unsigned 8-bit integer, and is often the maximum value possible for things in video games.
 * Mettaton and Napstablook are the only enemies in the game that use the Gray Attack.
 * Mettaton is a literal "ghost in the machine." This philosophical phrase is a critique of the perception that mind and body are separate entities when they are actually not comparable; a physical entity cannot be compared to an abstract one.
 * The Mettaton EX fight, according to Toby, was the hardest one for him to design. There were many attack ideas for the Mettaton EX fight that were never used, such as more tiny Mettaton robots, and disco dancing robots that threw stars.
 * Mettaton has the most songs relating to a single character in the game.

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