Mega Gross Set by Pinsir's Pincer

This Meta is Gross (Metagross-Mega) @ Metagrossite
Ability: Clear Body
EVs: 252 HP / 28 Def / 100 SpD / 128 Spe
Impish Nature
- Thunder Punch
- Iron Head
- Zen Headbutt
- Ice Punch

128 speed evs let it outpace max speed jolly mega gyarados.
Max HP increases the overall bulk. 28 Defense EVs and an Impish nature let it only get 2HKO'ed by a +1
Crunch from a max atk adamant gyarados:
+1 252+ Atk Mold Breaker Gyarados-Mega Crunch vs. 252 HP / 28+ Def Metagross-Mega: 306-362
 (84 - 99.4%) -- guaranteed 2HKO
and if gyarados tries to crunch mega gross twice, as much
as it 2hko'es it will get out sped and 2hko'ed by mega metagross' thunder punch.
The rest of the EVs are invested in Attack to increase the chances of Thunder Punch to KO Mega Gyarados.