Hayden's Metagross

Hayden's Metagross is the seventh Pokemon obtained by Hayden in the Hoenn region.

Hoenn
Hayden first obtained Metagross as a Beldum when Steven Stone gave it to him as a gift. This Beldum was then placed on Hayden's team while he headed for the Battle Frontier Island.

Battle Frontier
It was later revealed that Beldum had already evolved into a Metang where it battled Hayden's Shiftry in a practice battle. It is also revealed to have learned Metal Claw, Confusion, and Meteor Mash as well. But it was unable to perfect Meteor Mash.

In The Pikachu Reversal, it battled Red's Pikachu while readying for the Battle Pike. It managed to master Meteor Mash right before Pikachu was diagnosed with an overdose of Thunder. Metang managed to take a Thunderbolt and evolved into Metagross, saving it with a newly-learned Hyper Beam.

Metagross was then used against Pike Queen Lucy's Seviper at the Battle Pike where it had a good advantage due to Poison-typed attacks having no effect on a Steel-type at all. Using its powerful Meteor Mash, it managed to defeat Seviper before losing to her Milotic.

It was used again during the battle with Spenser where it took down his Crobat and lost to his Arcanine after Shiftry. Spenser claims that Metagross likes to take hits from attacks headon and has a mysterious bond with its trainer.

Metagross was placed at the Petalburg Gym under Norman's care while Hayden traveled to the Sinnoh region.

Sinnoh
Metagross was sent back to Hayden's team to train for the Sinnoh League. Metagross was seen using Gyro Ball under Hayden's command. Metagross was used against Marcus's Gengar in the third round of the tournament. Utilizing its Meteor Mash and Gyro Ball attacks, it manages to use Flash Cannon to block Gengar's Sludge Bomb and defeated it before losing to Empoleon.

Trivia

 * Metagross is the only Pokemon that wasn't used in the Hoenn League. Which meant that Metagross was obtained after Hayden defeated the Battle Frontier, which happened after three years later.
 * Metagross is the first genderless Pokemon owned by Hayden, the second is Golett.
 * Metagross is the only Steel-type to be owned by a main character.