|Status:||Varies based on route|
|Relationships:||Alphys (friend, "creator"), Napstablook (cousin), Mad Dummy (cousin), Burgerpants (employee), Bratty & Catty (fangirls)|
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Mettaton is the final boss of the Hotland area. He arrives to challenge Frisk multiple times, having them appear as a guest on his various TV shows, under the guise of being "out of control" so that Alphys will be able to grow close enough to Frisk to appeal to them to stay in the Underground. However, his relationship with Alphys is strained due to her procrastinating on finishing the humanoid upgrade to his body that he desires, and he eventually goes off-script and tries to kill Frisk for real. He states that he wants to keep Frisk's soul for himself to keep humanity safe from Asgore Dreemurr, and wishes to cross the Barrier to become a star in the human world as well. Toby Fox has stated that his boss battle has elements inspired by Jojo's Bizarre Adventure.
If spared, he reconsiders his plan after his cousin Napstablook calls in to his show, and realizes that the monsters still need him. He runs out of batteries and can no longer be interacted with until the True Pacifist ending, but can be found in Alphys' lab on her work desk nonetheless.
In Neutral endings where both Toriel and Undyne are dead, Mettaton becomes the new leader of the Underground, forcefully attempting to cheer up the people by taking over the entertainment industry. He is portrayed as a corrupt ruler who makes anyone who speaks against him disappear.
In a Genocide/No Mercy run, Mettaton blocks the way into the castle in a unique form, but cannot attack and is dispatched in one hit.
Mettaton's past as a ghost can be learned about if the player gets the key to his old house and reads his diaries.
Deltarune's version of Mettaton appears as one of the denizens of Hometown. Due to this world's Alphys being a teacher instead of a scientist, he does not have his robot body, and instead lives with Napstablook. He is a shut-in and refuses to either leave the house or to let Kris in if the player tries to say hello to him.
Most fanart of Mettaton portrays him in his humanoid body instead of his initial form.
Mettaton is often perceived by fans to be a transgender character based on Undyne referring to his old identity with they/them pronouns, and the otherkin community also treats him as an otherkin character.
- Mettaton/Papyrus (Papyton)
- Mettaton/Burgerpants (Mettapants)
Some fans take issue with the "Undertale: The Musical" event where Mettaton wears a dress and sings a ballad in parody of the Final Fantasy VI opera scene, based on the suspicion that the main "joke" of this event is supposed to be the fact that Mettaton is wearing a dress and not the parody elements and accusing the text of transmisogyny. Fans who disagree often point to the NPC known as "Dress Lion", who appears in this area after that event and says that seeing Mettaton wear a dress has emboldened them to try wearing one too. (In the True Pacifist epilogue, this character is seen wearing Mettaton's dress, which he has given to them.)
Mettaton is also the subject of ship wank, with anti-shippers claiming that Mettaton should not be shipped with Papyrus because Papyrus is "too innocent" to be shipped, and that Mettaton should not be shipped with Burgerpants because it "promotes abuse" due to Burgerpants' complaints about his boss. Wank about Mettaton/Burgerpants also claims that the pairing adheres to homophobic stereotypes of gay men using their positions of authority to sexually harass employees.
Undertail fanwork portraying Mettaton sexually sometimes attracts truscum wank if he is portrayed as having a vagina or interchangeable genital parts/if in human AUs he is portrayed as a pre-op or non-op trans man, on the basis that this is fetishization. Fans who make these kinds of complaints unfortunately tend to ignore when actual trans creators produce this kind of work. In worst case scenarios, this can turn into gatekeeping harassment targeting those creators for being trans "wrong" and/or accusing them of lying about their identities.
- make up my heart - oryx
- Metal Heart - MiniNephthys
- bonetrousled by glamour - simplycarryon (Mettaton/Papyrus)
- Oh! One True Love - loopy-lupe