How heavy is Mewtwo?

The figure is the Pokédex weight that the games and pokemon.com give for Mewtwo: 122 kg, or 269.0 lb, at a height of 2.0 m (6 ft 7 in). The same numbers appear in Pokémon Legends: Z-A and in Pokémon GO.

Pokémon GO's Armored Mewtwo, which wears the armor from the film Mewtwo Strikes Back, is listed at the same 122 kg and 2.0 m, so the armor adds nothing on paper.

Mewtwo can Mega Evolve in two ways. With Mewtwonite X it becomes Mega Mewtwo X, a Psychic and Fighting type that grows to 2.3 m and 127 kg (280.0 lb). Its Pokédex entry says psychic power has built up its muscles, giving it a grip strength of one ton.

With Mewtwonite Y it becomes Mega Mewtwo Y, which goes the other way: 1.5 m tall and only 33 kg (72.8 lb), about a quarter of its normal weight. The Pokédex says its mental power grows even as its body shrinks.

Mewtwo was created by recombining the genes of Mew, and the Yellow Pokédex points out that its DNA is almost the same but its size is vastly different. The numbers bear that out: Mew is 0.4 m tall and weighs 4 kg, so Mewtwo is five times taller and about 30 times heavier.

Among the other legendaries of the original 151, Mewtwo is also the heaviest by a wide margin. Moltres weighs 60 kg, Articuno 55.4 kg and Zapdos 52.6 kg, so Mewtwo is about twice any of the three birds.

Low Kick and Grass Knot get stronger the heavier the target is. Mewtwo and Mega Mewtwo X both fall in the 100.1 to 200 kg band, so they take 100 power, one step below the maximum. Mega Mewtwo Y, at 33 kg, takes only 60.