Weak toFightingGroundFire ×1.6

Attacker	Type	Moveset	DPS
Blacephalon	FireGhost	IncinerateMind BlownLegacy	38.3
Lucario	FightingSteel	Force PalmAura SphereLegacy	32.5
Reshiram	DragonFire	Fire FangFusion FlareLegacy	31.8
Pheromosa	BugFighting	Low KickFocus Blast	29.7
Terrakion	RockFighting	Double KickSacred SwordLegacy	29.6
Blaziken	FireFighting	CounterAura Sphere	29.4
Chandelure	GhostFire	Fire SpinOverheat	29.1
Cinderace	Fire	Fire SpinPyroball	28.7
Volcarona	BugFire	Fire SpinOverheat	28.4
Darmanitan	Fire	Fire FangOverheat	28.3
Groudon	Ground	Mud ShotPrecipice BladesLegacy	27.3
Moltres	FireFlying	Fire SpinOverheat	27.1

Overcast boosts the Fighting attacks above. Overcast and Snow boost Mega Lucario.

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

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

Questions people ask

What is Mega Lucario weak to in Pokémon GO?

Mega Lucario takes 1.6 times from Fighting, Ground and Fire.

What's the best counter to Mega Lucario?

Blacephalon with Incinerate and Mind Blown, worth 38.3 damage per second against Mega Lucario's own defense. The full ranking is above.