It depends on the format you are playing and the moveset and EV spread you will want to be choosing. On more defensive sets in RU, particularly those that use Stealth Rock, Leftovers is almost always seen. You are likely hurting yourself by not using Choice items on a more offensively-focused Metagross rather than a mix between defensive utility and offensive support, as shown by the brutal power of Choice Banded Zen Headbutts and the solid speed control the Choice Scarf set provides. Life Orb on Metagross is kind of rubbish since with Metagross's rather low Speed stat compared to the rest of the offensive metagame, it will probably be taking a hit first, and the extra recoil doesn't help with the longevity.
Metagross @ Leftovers
Ability: Clear Body
EVs: 252 HP / 124 Atk / 76 SpD / 56 Spe
Adamant Nature
- Meteor Mash
- Earthquake
- Stealth Rock
- Toxic
Metagross @ Leftovers / Weakness Policy / Life Orb
Ability: Clear Body
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Meteor Mash
- Earthquake
- Agility
- Zen Headbutt
In Battle Stadium formats, since Metagross has the ability to Dynamax, a Weakness Policy works exceptionally well on Metagross. This is because Metagross's weaknesses are not hard to come across (especially in Doubles, where you have things like Incineroar and Landorus-Therian going crazy), and its already good bulk + an Intimidate immunity in Clear Body make it one of the Weakness Policy's best users in Battle Stadium Singles and a good pick in VGC 2021. Assault Vest can also be used because of all the Special moves flying around too, and Metagross's Defense stat is already great, so it can work well.
