Weak toFlyingPoisonBugFireIce ×1.6

Attacker	Type	Moveset	DPS
Blacephalon	FireGhost	IncinerateMind BlownLegacy	33.5
Eternatus	PoisonDragon	Poison JabDynamax CannonLegacy	28.7
Reshiram	DragonFire	Fire FangFusion FlareLegacy	27.8
Pheromosa	BugFighting	Bug BiteBug Buzz	26.1
Salamence	DragonFlying	Fire FangFly	25.7
Chandelure	GhostFire	Fire SpinOverheat	25.5
Moltres	FireFlying	Fire SpinFly	25.3
Cinderace	Fire	Fire SpinPyroball	25.1
Enamorus	FairyFlying	Fairy WindFly	25.0
Volcarona	BugFire	Fire SpinOverheat	24.9
Darmanitan	Fire	Fire FangOverheat	24.8
Yveltal	DarkFlying	GustOblivion WingLegacy	24.7

Clear boosts the Fire attacks above. Clear boosts Meganium.

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

Meganium's moveset, CP and shiny All counters Raid board

Questions people ask

What is Meganium weak to in Pokémon GO?

Meganium takes 1.6 times from Flying, Poison, Bug, Fire and Ice.

What's the best counter to Meganium?

Blacephalon with Incinerate and Mind Blown, worth 33.5 damage per second against Meganium's own defense. The full ranking is above.