Mettaton, sometimes shortened to MTT, is a robot designed to destroy humans and was introduced in the 2015 RPG Undertale. They were designed by Alphys to help Asgore destroy humans.
Mettaton's most recognizable form, Mettaton changes from its robotic "calculator" like appearance to a much more human like one, giving it new attacks, ranging from leg attacks to disco balls firing lasers. It has a huge loss of durability, yet makes up for it with power. He is 6'4".
Dr. Alphys' ultimate creation. It contains all of Mettaton's programming from when he was designed as a human-hunting robot, and is his most powerful form as a result.
Not much is known about this form except a new design, and a cannon on one of his arms, because Chara easily took Mettaton NEO out with a single hit.