UNDERTALE/Mettaton

Overview
Mettaton is a robot with a SOUL that appears in the HOTLANDS. He is like Chara, in the sense that they both hate humanity, even if for different reasons. Chara hating humanity for reasons unknown, and Mettaton because it was a part of Alphys's plan.

Mettaton 1st Form
In his 1st form, Mettaton is a TV screen with a wheel. That's it. The TV screen has 5×4 grid that he can make different things with on it, but that's just about it.

Mettaton EX
Mettaton EX looks... human (ironic since he hates humans). After having the switch on his back flipped in the 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 pads 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
Mettaton NEO is just like the EX form, except he is more battle oriented. He has a cannon for an arm, huge spiky wings on his back, huge, dorky pauldrons on his shoulders, and now he wears black high heels. Thankfully, this only appears in Genocide Route (and he dies in one hit), because if this was real, this would be a NIGHTMARE to fight.

Personality
Mettaton is a confident, charismatic, and charming TV host that loves drama, action, and violence. He shows a rather shallow appreciation for existence at times. He has a strong craving for attention and is very egotistical for the point of narcissism. However, despite his seemingly narcissistic personality, he deeply cares about the seemingly positive impact his show has had on the inhabitants of the Underground. He has also shown soft spots for several characters, such as Alphys and Napstablook. He also appears to be among the fewer characters in the Underground that has no hate or prejudice against humans despite knowing about the monsters' history with them, since his initial attempts to kill the protagonist were just him playing along with Alphys's plan, and he outright tells the protagonist he has no desire to hurt humans and is far more interested in simply entertaining. While he did attempt to kill the protagonist, it was to prevent Asgore from taking their SOUL and be seen as a hero/savior to humankind, further emphasizing his lack of prejudice.

Pacifist Route
He appears after Alphys explains what he "accidentally" did to Mettaton. He goes on to give the player a large amount of puzzles before and during the core. He is seen at the end of the game before Flowey becomes Asriel.

Neutral Route
Same as above. Solve the puzzles, defeat the humanoid robot, you know what to do.

Genocide Route
He dissappears as soon as the player comes to Alphys's lab. He then appears at the end of the core like normal, but as Mettaton NEO. He dies in one hit, however. Wow, how amazing. The great Mettaton NEO, the one who could kill a guy with a single attack... and he dies in one hit.

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?".
 * It is impossible to name the player "Mettaton" unless the game is hacked, although the result might be the same as the names above.
 * 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 Judeo-Islamic 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."
 * "Mettaton" may be a portmanteau of "Meta" and "ton," as Mettaton offers many instances of meta-commentary on the structure of Undertale.
 * 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.
 * Notably, Mettaton NEO can be encountered in an aborted Genocide Route (Alphys Ending, Near Genocide) unlike Undyne the Undying.
 * Both of their forms on the Genocide Route feature hearts on their chest pieces.
 * Both of their battles on the Genocide Route feature the Battle Against a True Hero leitmotif.
 * Undyne holds a spear in her right hand, and Mettaton NEO has an arm cannon replacing his right hand.
 * In his box form, Mettaton's overworld sprite has five squares under the main screen, while his battle sprite only has 4.
 * Mettaton has the most songs (14) associated with him.
 * He actually has 15 if the CORE music is counted
 * 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.