Mettaton

Mettaton is a robot with a soul built by Alphys, initially acting as a human hunting machine but it is later revealed that he is the sole television star of the Underground.

Initial Form
In Mettaton's initial appearance, he appears as a grey, largely rectangular box with a grid of lights at the top which can change color depending on his various actions. He has four dials along the bottom of his body, and from 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 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 fringe that covers his right eye, pale "skin", and visible metal segments below and above his left eye.

He has a pink chest piece with a dial on one side and a speaker on the other, a narrow metallic waist which holds his soul upside down, and black shoulder guards above his segmented arms, which end in gloves. His long black-clad legs end in pink 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, his shoulders are clad in pauldrons, 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 in his chestplate 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 and charming TV host, that loves drama, action, and violence. He lives for his ratings and loves performing. He supposedly strikes a pose when he does something wrong and makes time on his various shows for beating up "heel-turning villains". He shows a rather shallow appreciation for existence at times. In spite of his seemingly vain personality, he deeply cares about the 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 busts 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. 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 does very high damage. Alphys on the top right will give answers via hand motion; realizing this, Mettaton chooses to humiliate her by quizzing the protagonist on the identity of her unrequited love interest. Ultimately however Mettaton departs, concluding that the quiz show has lost all dramatic tension.

As the protagonist journeys through Hotland, Mettaton entraps them in deadly pastiches of various media genres. First up is a cooking show where Mettaton is preparing a dish with a human soul as the main ingredient. Alphys calls up 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 substitute on top of a faraway cupboard.

However, the cupboard begins to rise from the ground at a rapid rate, forcing the protagonist to use the jetpack feature installed on their phone by Alphys to fly to the top and retrieve the substitute within a time limit set by Mettaton. If the protagonist reaches the substitute within the time limit, Mettaton states 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 while there are no viewers. Either way, he comments that he was foiled by Alphys. Secondly comes a breaking news segment in which the protagonist is asked by Mettaton to report on one of several items within a room, 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' 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 will now explode in two seconds. Regardless of whether the bombs were defused or not, Alphys hacks the big bomb and disables it.

Thirdly and finally Mettaton traps the protagonist within a musical, where Mettaton will sing about a forbidden love between him, a monster, and the protagonist, a human. He will mention 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. If the protagonist manages to complete the puzzle, Mettaton deactivates the flames "knowing" that Alphys would have done so anyway. If the protagonist fails, the flames draw near, only for Alphys to disable them. If they had failed and attempted the puzzle and 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 fails but 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 anyway.

Mettaton proceeds to engage the player after the tile puzzle. However, Alphys has one final installment on the phone she had given to the protagonist. This yellow button fires projectiles at Mettaton, who acts defeated and flees.

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 legitimately kill the protagonist. 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 further ally herself with the protagonist; Alphys plans to intervene the fight between Mettaton and them by 'deactivating' Mettaton and thus appearing heroic to them. This time however, Mettaton has made plans to prevent Alphys' aid, so that he could have a sincere 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 could 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 (now urgent) 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 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 (12,000 if he still has limbs), 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 entertainment that many of the inhabitants of it 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 potentially 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.

Mystery Key
If the protagonist purchases the Mystery Key from Bratty and Catty, they can enter the house to the right of Napstablook's. 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 name was Happstablook, which isn't wrong, it's his headcanon). After meeting Alphys, she designed a body for Mettaton to inhabit, and that this ghost inhabits Mettaton's body.

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 Boss Monsters have united before Flowey intervenes, Mettaton EX shows his leg from the 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 will be seen standing outside Napstablook's cousin's house, having recruited Napstablook as his sound mixer and Shyren as their back-up singer. During the credits, he's shown on tour, able to use his original box form in conjunction with his new body's legs.

Genocide Route
Mettaton will show up once the protagonist reaches Alphys's house and then tell them that he won't battle them, knowing that he's no match for them. He shows up at the Core and realizes that the protagonist's path of destruction means to not only 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 player can destroy him in a single attack.

The Genocide Route will continue only if all monsters in the Hotland/Core area have been killed. If this is not the case, Mettaton will point out the protagonist's lack of killing intent, telling them that they aren't 'absolutely evil' before dying. This changes the route to the Neutral Route, and completing the run will result in a call from Alphys instead of Sans.

In Battle

 * See Mettaton/In Battle.

The Protagonist
Initially, Mettaton actively antagonized the protagonist under the assumption its directive error'd into giving it an intense 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 own terms in order to take their SOUL to prevent a possible war by Asgore. After their battle, however, he was confident the protagonist was strong enough to prevent 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 though, 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 own 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 as he 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.

Name
"Mettaton" is similar in pronunciation and spelling to "Metatron", the highest angel in Jewish lore, transliterated into greek as MTT. It could also be a portmanteau of "metal" and "automaton".

If "METTA" or "METT" is typed for the Fallen Child's name, the response becomes "OOOOH!!! ARE YOU PROMOTING MY BRAND?".

Trivia

 * Mettaton's design is similar to other characters not belonging to Undertale.
 * Mettaton's normal form resembles the coin-operated robot Cooker from the Wallace and Gromit short "A Grand Day Out".
 * His form also bears resemblance to the Craniac robots of ChalkZone fame.
 * The shape of Mettaton EX's body is very similar to Klaus Nomi, a well-known German countertenor's outfit.
 * Mettaton is at least partially inspired by Twitter user nerdbotmk2.
 * Mettaton NEO resembles Super Bass from the Mega Man series.
 * 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 colored-tile maze will play the same "Yeah" when Mettaton EX is attacked.
 * The answers to the question What are robots made out of? in his quiz show have several references.
 * "Hopes&Dreams" references the track "Hopes and Dreams"
 * "Snips&Snails" and "Sugar&Spice" are references to the nursery rhyme "What Are Little Boys Made Of?"
 * Mettaton's box form is identical to the colored tile maze machine found in Snowdin.
 * During Mettaton's singing performance to the protagonist, the program window is renamed to "UNDERTALE the Musical".
 * Mettaton EX has responses for "sexy", "foxy", and "tantalizing" in his essay question, but since the X and Z keys can't be inputted, they're not accessible in-game.
 * 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 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 how Mettaton and Napstablook are suddenly included in the full menu.