Agility / Body Slam
Metagross is an oddity among Psychic-types. Unlike most of them, he's a Physical attacker, and has huge physical defense. His Special is mediocre but usable. This makes Metagross work differently from other Psychic-types, instead of abusing Psychic offensively, Metagross attempts to be a Psychic Counter due to his OK 90 Special and his amazing 135 attack hitting Psychic's on their lower defense, while also resisting Psychic. Metagross's biggest downfall is probably it's average speed and mediocre HP stat. Still, for a heavily defensive pokemon, Metagross is decently fast, and has Agility to patch up his speed. RockQuake gives great coverage and hits Psychics on the weaker defense, while Psychic is STAB and comes from his decent 90 Special. Agility is to patch up his speed and try to crit afterwards, as after an Agility Metagross is decently fast. Meanwhile, Body Slam has a nice 30% paralysis chance, allowing Metagross to be more of a team player. He also has access to BoltBeam in the form of Thunder/Ice Punch, but their 75 BP plus his 90 Special make them underwhelming unless they hit SE. His Defense really shines due to the lack of relative weaknesses.