Metagross has the appearance of a tremendous, quadrupedal tank-like Pokémon. Its turquoise-colored, discus-shaped main body appears to be its head, as it lies at the center point where its legs branch out to give the impression of a mechanized arachnid. Each leg could be viewed as the body of a former Beldum, and its head/body as the four collective heads of Beldum used to fuse into it. Metagross has a metallic cross adorning its face formed by its tusks crossing diagonally between its two red eyes, often viewed as the letter "X" by onlookers, and this cross-shape is arranged to resemble both metallic "eyebrows" and a metallic "mustache." This is said to represent Metagross's wise, computative nature.
In the same way that its pre-evolved form Metang is comprised by two Beldum, a still more basic evolution stage, so is Metagross formed by the joining of two Metang. This essentially means that four Beldum make up a Metagross (this could be compared to Magneton or Magnezone, both of which are comprised of 3 Magnemite). However, four Beldum come nowhere near to the size of a Metagross.
Metagross is a genderless species.
Metagross's intelligence is extraordinarily high: not only does it have four brains (one from each Beldum) but they are also connected by a highly complex neural network. Its developed cerebral powers are said to surpass even those of a supercomputer, similar to Alakazam. As a Psychic-type Pokémon, it can also use psychic abilities, including the ability to render its massive body airborne by telekinesis once it draws its legs together. Metagross's movepool isn't that much different than its predecessor, Metang. The only two moves that Metagross can learn that Metang lacks are Hammer Arm and Giga Impact.
Possessing four brains, Metagross is an extremely wise Pokémon with unmatched intelligence. However, it is known to be a vicious predator-using its weight, it traps its prey under its body and devours them. Some are very aggressive and territorial of their homes and will not hesitate to attack intruders that trespass.
This Pokémon lives in mountainous areas along with its evolutionary lines, but are even rarer than their pre-evolutions. It can easily live comfortably on very steep slopes by planting its legs into rock or ground. They can occasionally be found in Giant Chasm.
A wild Metagross appeared in Regaining the Home Advantage!, where it battled non-stop with a Magnezone. These two Pokémon normally battled with each other on a regular basis until their "battle arena" (a deep crater) became filled with water. Because their crater was no longer usable, they took their battle to the streets of a nearby town, and continued fighting, causing much collateral damage.
Steven in Pokémon Adventures owns a Metagross. It's his flight Pokémon, carrying him from place to place with its levitation abilities. He also owns a Metang and many Beldum, which, along with his Metagross, help dig out and find rare stones in caves.
Tucker also mentioned of having a Metagross which has yet to be seen.
Upon its release from its Poké Ball, it will stay in one place and repeatedly use Earthquake. Anyone caught underneath the Pokémon will be buried into the ground and thus unable to move for a few moments, until Metagross uses its attack and all the hit characters are blasted upwards.
Metagross was featured as one of the Pokémon released from a Poké Ball in the demo of Super Smash Bros. Brawl at Jumpfesta; however, it hovered above the stage before attacking, unlike in the actual game.
"An Iron Leg Pokémon. When two Beldum combine, they evolve into Metang. In the same way, Metagross is the result of two Metang combining. It's said to have the intelligence to match a supercomputer. Though it weighs 1,212.5 pounds, it is somehow able to fold up its legs and float."
This Pokémon was unavailable prior to Generation III.
Metagross is the result of two Metang achieving fusion. When hunting, this Pokémon pins the prey to the ground under its massive body. It then eats the helpless victim using the large mouth on its stomach.