Weak toFightingBugGrassElectricFairy ×1.6

Attacker	Type	Moveset	DPS
Regieleki	Electric	Lock OnThunder CageLegacy	35.4
Lucario	FightingSteel	Force PalmAura SphereLegacy	31.6
Pheromosa	BugFighting	Bug BiteFocus Blast	30.8
Kartana	GrassSteel	Fury CutterLeaf Blade	30.5
Zeraora	Electric	Volt SwitchPlasma Fists	30.4
Zekrom	DragonElectric	Charge BeamFusion BoltLegacy	29.7
Xurkitree	Electric	Thunder ShockDischarge	29.3
Terrakion	RockFighting	Double KickSacred SwordLegacy	28.8
Blaziken	FireFighting	CounterAura Sphere	28.6
Tapu Koko	ElectricFairy	Volt SwitchNatures MadnessLegacy	27.8
Breloom	GrassFighting	Force PalmGrass KnotLegacy	27.2
Enamorus	FairyFlying	Fairy WindDazzling Gleam	26.7

Rainy boosts the Electric attacks above. Fog and Rainy boost Mega Greninja.

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

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

Questions people ask

What is Mega Greninja weak to in Pokémon GO?

Mega Greninja takes 1.6 times from Fighting, Bug, Grass, Electric and Fairy.

What's the best counter to Mega Greninja?

Regieleki with Lock On and Thunder Cage, worth 35.4 damage per second against Mega Greninja's own defense. The full ranking is above.