Mega Metagross set

[Black117]

As of right now, both jolly and adamant remain as the best natures for Mega Metagross depending on a particular set/build. If you are going with singles, here are the main sets:

Metagross @ Metagrossite
Ability: Clear Body
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Meteor Mash/Iron Head
- Zen Headbutt
- Bullet Punch/Ice Punch/Pursuit
- Earthquake/Hammer Arm

or the Classic Agility/Rock Polish Set

Metagross @ Metagrossite
Ability: Clear Body
EVs: 80 HP / 252 Atk / 176 Spe
Adamant Nature
- Rock Polish
- Iron Head/Meteor Mash
- Zen Headbutt
- Earthquake

As far as doubles are concerns: I have an experimental metagross set here.