This page contains spoilers.
Mettaton is a robot created by Alphys as an entertainment bot that is haunted by a ghost. She later altered his design to be more pleasing to the ghost that inhabits the shell. The ghost is Napstablook's cousin and used to live next door to him. The pink house can be entered by using the Mystery key obtained from Bratty and Catty. Inside is a diary collection, each book has a single entry. One of the entrys talks about how they promised to not leave Napstablook and Shyren. He has the Celebrity role.
In a neutral/pacifist route, Alphys claims that she altered Mettaton's design to make him a human hunter and that something went wrong with the AI programming. During Hotland, Mettaton encounters the human on multiple occasions to 'fight' them. The entire thing is a play of Alphys's devising to try to make the player consider her a hero. In actuality, there are no punishments if you do literally nothing during the Mettaton segments in Hotland (excluding giving him the eggs, milk, flour and attempting to give him the human soul replacement for the cake). You can fail the jetpack minigame, the bomb defusing minigame and the colour puzzle without any repercussions what so ever. There are even situations where Alphys forgets her line and Mettaton just says it instead.
By the time you reach the core, Mettaton is sick of playing along (actually he gets sick of it just before you encounter Muffet because he's the one who paid her and the mercenaries to kill you). He rearranges the CORE and deactivates the elevator so Alphys's deception becomes obvious. He then outright explains to the player what Alphys has been doing. His plan is to steal the soul of the player so he can pass through the barrier and become a star on the surface. The battle is televised.
During the Genocide route, Mettaton genuinely is changed into a human killer. He claims that he was originally created for this purpose and was changed into an entertainment bot afterwards, the opposite of what Alphys says in a pacifist route so there is some debate over which is the true version. The fight is laughablly short with the backing track being only around 30 seconds long. A full Genocide is not required to encounter Mettaton NEO, the Hotland and CORE kill counts don't need to be exhausted, but Undyne the Undying must be encountered and killed.
Mettaton is a box-like robot with a 4X5 grid of coloured squares. The grid displays an M, a ! and a heart as well as flashing different colours, mainly red and yellow. On a Neutral/Pacifist route Mettaton is turned into his EX form after hitting a switch on Mettaton's back. After activating the EX form, the ghost in Mettaton becomes corporeal like the Mad dummy does in the Genocide run. Mettaton NEO is the form encountered on a Genocide/aborted Genocide run.
The standard Mettaton form is indestructable but has a weapon that only halves the remaining HP of the player. It is unknown if they can kill anything in this form.
The EX form can be broken. The yellow soul is used during his fight.
- Miniture versions of Mettaton descend from the top of the screen and throw hearts at the human
- A discoball that shows blue and white attack lines that change colour when the ball is shot.
- The box becomes very thin with a bomb and an indestructable box descend from the top of the screen, the bomb must be shot and the the blast dodged, then the box dodged.
- Mettaton's legs appear at the side of the box, kicking the player if they haven't moved out of the way of the warning.
- A large number of multiple attacking items descend from the top of the screen, all must be dodged.
- A series of things descend form the top of the screen which the player shoots to get past. The 'footage' is the reversed, sending the series of attack backwards. The player must remember where the gaps are from the footage moving forward.
- Mettaton reveals their soul which zaps the player while protecting itself with boxes. Shooting the soul is optional, Mettaton looses limbs whether or not he is shot during this segment.
- There is also an essay section during which writing certain words give a huge boost to views. Legs gives the highest viewer boost of 350 with Toby being the second highest of 300.
- Heel turn
- You turn and scoffed at the audience, they are rooting for your destruction this turn!
- The number of viewers increase if you are hurt by Mettaton during his turn.
- You say you aren't going to get hit at ALL. Ratings gradually increase suring Mettaton's turn.
- The number of viewers increase during Mettaton's turn but drop by a large amount if struct.
- (varies depending on HP)
- You posed dramatically. The audience nods. [pose]
- Despite being hurt, you posed dramatically. The audience applauds. [pose with <1/2 HP]
- Despite being wounded, you posed dramatically. The audience gasps. [pose with <1/4 HP]
- With the last of your power, you pose dramatically. The audience screams. [pose with very low HP]
- The number of viewers gained during the fight is inversely proportional to the amount of HP the player has. It's between 100-1000.
- (varies depending on HP)
- Changeing the equipment the human is wearing to something that hasn't be worn yet in the fight, gives a viewer boost.
- Eating food from the MTT-Brand Burger Emporium gives a viewer boost.
- Throwing the stick will give a boost but only once. This boost is doubled if Mettaton has lost his arms and legs.
- Getting hit will give a viewer boost but the boost it gives is reduced very quickly.
- Hitting Mettaton will give a viewer boost but only the first time he is hit.
- Shooting things during Mettaton's turn gives a small increase in viewers.
- Don't type swear words during the writing custom essay, that decreased the number of views.
- Don't eat junk food during the fight, that also decreases the number of views.
- Reducing the number of views in necessary if the player wants to kill Mettaton as they will likely achieve everything needed to spare him before taking down his HP.
The NEO fight is laughably easy and very short. He has no attack patterns and is always killed in a single blow. The backing track 'The power of NEO' is just over 30 seconds long.
AUs Mettaton is in:
- Undertale Rho