Mettaton

Mettaton is a robot built with a soul (heavily implied to be that of Napstablook's cousin) by Alphys, initially as a human hunting machine but later becoming the sole television star of the Underground.

The name Mettaton appears to be derived from Metatron (or sometimes Mattatron), an archangel in Judaism whose name is transliterated into Greek as MTT. This name doubles as a play on the word "automaton" which is a moving mechanical device made in imitation of a human being, and additionally sounds somewhat like "metal" which is what Mettaton is made from.

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.

This form greatly resembles the color tile puzzle that was also developed by Alphys. It may in fact be possible that the puzzle literally was Mettaton the entire time, given his knowledge of the player's prior experience with the puzzle and the fact that the initial machine is gone if the area is traveled back to after Mettaton has already been encountered.

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, a dial on one side and a speaker on the other, and a narrow metallic waist which holds his soul (or what he describes as a heart), 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 Run, Mettaton transforms into Mettaton NEO, which resembles Mettaton EX, but has an obviously more combat-oriented design.

The front section of his right arm is replaced by what appears to be some form of gun, and both of his arms are clad in black pauldrons like the rest of his suit. The heart or soul on his waist is upside down in a more monster-like manner, and he has a heart shape engraved in his chestplate like Another Genocide Route exclusive boss.

His hair on the right side is spiked out to the side, revealing a segment of his face which is entirely black but for what appears to be a sparkle where the right eye would normally be, mirroring the hidden right eye of his EX form.

Personality
Mettaton is a confident and charming TV host, that loves drama, action, and violence. He lives for his ratings and loves performing. He shows a rather shallow appreciation for existence at times, as referenced in various neutral endings.

Beyond this, however, he sincerely cares for humanity and monster-kind, even mentioning Alphys specifically on multiple occasions.

Pre-Game
Various evidence in the game implies that the monster's soul within Mettaton is that of a ghost known only as "Napstablook's cousin" within the game (though Papyrus states that his name was Happstablook, which isn't wrong, it's his headcanon), who lives in the house next to Napstablook's. As a ghost, Mettaton expressed a keen interest in humankind, and at some point met Alphys in a human fan club. Alphys became fast friends with them and at a later point used them in her first experiments with the soul to create a robot with a soul.

Neutral/True Pacifist Route
When meeting Alphys in the Lab, the player 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 player for some time) and forces the player 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; realising this, Mettaton chooses to humiliate her by quizzing the player on the identity of her unrequited love interest. Ultimately however Mettaton departs, concluding that the quiz show has lost all dramatic tension.

As the player 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 player's soul as an ingredient, so instead Mettaton points towards a substitute on top of a faraway cupboard.

The cupboard begins to rise from the ground at a rapid rate, forcing the player 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 player fails to reach the substitute within the time limit, Mettaton will claim that the show is on an ad break, and refuses to kill them while there are no viewers.

Secondly comes a breaking news segment in which the player 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 player 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 player fails to do this in time, Mettaton will give them an extra minute.

Thirdly and finally Mettaton traps the player within a Broadway musical, where Mettaton will sing about a forbidden love between him, a monster, and the player, a human. He will mention how sad it is that the player must be sent to the dungeon, before opening a trapdoor underneath them into a room with a coloured tile puzzle. Mettaton announces that the player must pass the coloured tile puzzle within a set time before a line of flame comes at them from the side and burns them to death. If the player does not attempt the puzzle, Alphys will deactivate the flames and Mettaton will repeatedly say "well" before acknowledging that the player never stepped on a green tile, and for that must die.

After the player enters the Core and arrives at the final room before New Home, they are once more confronted by Mettaton. This time however, Mettaton reveals that he had re-arranged the Core so as to attempt to legitimately kill the player. He states that Alphys had set up an extensive plan to self-insert herself into the story, because she liked the player so much and wanted to feel important by helping them. All of the previous threats from Mettaton were entirely fake, and used by Alphys to further ally herself with the player; Alphys plans to intervene the fight between Mettaton and the player by 'deactivating' Mettaton and thus appearing heroic to the player. This time however, Mettaton has made plans to prevent Alphys' aid, so that he could have a sincere battle against the player, and locks the door to prevent Alphys from entering. He explains that he wants to take the Soul of the player 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 attacks the player in his original form, but under the (now urgent) advice of Alphys, the player tricks Mettaton to turn around so that they can press the button on his back. This changes 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 player is strong enough to potentially defeat Asgore. He then deactivates, armless - whether his arms 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 the player purchases the Mystery Key from Bratty and Catty, they can enter the house to the right of Napstablook's which is explained through a series diaries to be owned by the cousin of Napstablook. Also a ghost, this monster dreamed of being on the stage, and desired a 'unique' sort of body to inhabit. It is heavily implied that this ghost was the soul that was put into Mettaton's body (Mettaton refers to Napstablook as Blooky, as do the diaries inside of the house). 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 player 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 player reaches Alphys's house and then tell the player that he won't battle them, knowing that he's no match for them. He shows up at the Core and realizes that the player'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 this, he has no attacks, and the player can destroy him in a single attack.

The Genocide route will continue if the player has killed all monsters in the Hotland/Core area.

If the player hasn't killed every monster in the Hotland/Core area, Mettaton will point out their lack of killing intent, telling them that they aren't 'absolutely evil', and let them go. This changes the route to the Neutral Route, and completing the route will result in a call from Alphys instead of Sans.

In Battle

 * See Mettaton/Encounters

Frisk
Initially, Mettaton actively antagonized the player 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 players 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 player was strong enough to prevent this themselves. In the Genocide route, he will spare the player if they failed to kill every monster in Hotland and the Core up to that point and failed to deal the finishing blow on him, believing they aren't truly evil.

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 player. 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.

Similarities to other characters

 * Mettaton's normal form resembles the coin-operated robot Cooker from the Wallace & 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 apparently at least partially inspired by Twitter user nerdbotmk2, whose icon depicts a similar one-wheeled robot.

Trivia

 * Due to Mettaton's massive defense, any attack on him even if successful will display "Miss".
 * 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 once in his final battle.
 * "Oh My...", which plays before the Mettaton EX battle, is similar to the intro of "Killed by BR8K Spider!!!!!!!!", another song by Toby Fox.
 * If "METTA" or "METT" is typed for the character's name, the response becomes "OOOOH!!! ARE YOU PROMOTING MY BRAND?"
 * If the Mystery Key is used during Mettaton's battle, he will pretend it isn't there.
 * During the quiz show, one of the questions has the answer "Snips & Snails"; a reference to the nursery rhyme, "What Are Little Boys Made Of?" Another answer refers to "Sugar & Spice," which refers to similar nursery rhyme about what little girls are made of.
 * The answer "Hopes & Dreams" also references the song of the same name.
 * Mettaton can be seen early into the game as the console for Papyrus's tile trap, however, it is unknown if the machine actually was Mettaton himself or a console made in his likeness.