Weak toFightingGroundSteelWaterGrass ×1.6

Attacker	Type	Moveset	DPS
Lucario	FightingSteel	Force PalmAura SphereLegacy	19.1
Kartana	GrassSteel	Razor LeafLeaf Blade	18.2
Pheromosa	BugFighting	Low KickFocus Blast	17.4
Terrakion	RockFighting	Double KickSacred SwordLegacy	17.4
Blaziken	FireFighting	CounterAura Sphere	17.2
Metagross	SteelPsychic	Bullet PunchMeteor MashLegacy	16.6
Inteleon	Water	Water GunHydro CannonLegacy	16.4
Kyogre	Water	WaterfallOrigin PulseLegacy	16.4
Breloom	GrassFighting	Force PalmGrass KnotLegacy	16.4
Tinkaton	FairySteel	Fairy WindGigaton HammerLegacy	16.2
Groudon	Ground	Mud ShotPrecipice BladesLegacy	16.0
Conkeldurr	Fighting	Force PalmFocus Blast	15.9

Overcast boosts the Fighting attacks above. Partly cloudy boosts Regirock.

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

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

Questions people ask

What is Regirock weak to in Pokémon GO?

Regirock takes 1.6 times from Fighting, Ground, Steel, Water and Grass.

What's the best counter to Regirock?

Lucario with Force Palm and Aura Sphere, worth 19.1 damage per second against Regirock's own defense. The full ranking is above.