Weak toGroundGhostFireDark ×1.6

Attacker	Type	Moveset	DPS
Blacephalon	FireGhost	IncinerateMind BlownLegacy	23.9
Reshiram	DragonFire	Fire FangFusion FlareLegacy	19.9
Chandelure	GhostFire	Fire SpinOverheat	18.2
Cinderace	Fire	Fire SpinPyroball	17.9
Volcarona	BugFire	Fire SpinOverheat	17.8
Darmanitan	Fire	Fire FangOverheat	17.7
Darkrai	Dark	SnarlShadow Ball	17.4
Gengar	GhostPoison	LickShadow BallLegacy	17.2
Blaziken	FireFighting	Fire SpinBlast BurnLegacy	17.1
Groudon	Ground	Mud ShotPrecipice BladesLegacy	17.1
Moltres	FireFlying	Fire SpinOverheat	16.9
Absol	Dark	SnarlBrutal SwingLegacy	16.9

Clear boosts the Fire attacks above. Snow and Windy boost Mega Metagross.

Level 40, 15 attack IV, costed against Mega Metagross's own defense and typing, one per evolution family.

Mega Metagross's moveset, stats and CP All counters Raid board

Questions people ask

What is Mega Metagross weak to in Pokémon GO?

Mega Metagross takes 1.6 times from Ground, Ghost, Fire and Dark.

What's the best counter to Mega Metagross?

Blacephalon with Incinerate and Mind Blown, worth 23.9 damage per second against Mega Metagross's own defense. The full ranking is above.