I heard that people actually use Zen Headbutt Metagross and Bounce Gyarados in CAP. Is this true?
This is very true, as a matter of fact. Metagross and Gyarados have been hindered offensively by Arghonaut, whose high HP and Defense makes it difficult for Metagross to overcome, even with ThunderPunch, while Gyarados’s Dragon Dance boosts are instantly ignored due to Unaware. This has led to the increase of popularity in Zen Headbutt for Metagross, especially on Agility sets. With Zen Headbutt, Metagross is now capable of 2HKOing Arghonaut and is no longer stopped dead in its tracks; in fact, Metagross threatens Arghonaut. On the other hand, Bounce is the only way for Gyarados to deal with Arghonaut, even though it isn’t the most reliable method, due to it being able to Recover as Gyarados charges for the Bounce. With Bounce, Gyarados can safely accumulate several Dragon Dance boosts and is not instantly countered by Arghonaut, who must face powerful STAB Bounces that may end up paralyzing it. That’s about all we’ve got to say, at least for now. There’s no doubt that there are some t