Weak toGroundGhostDark ×1.6

Attacker	Type	Moveset	DPS
Blacephalon	FireGhost	AstonishShadow Ball	33.8
Darkrai	Dark	SnarlShadow Ball	30.4
Chandelure	GhostFire	HexShadow Ball	30.1
Gengar	GhostPoison	LickShadow BallLegacy	30.1
Groudon	Ground	Mud ShotPrecipice BladesLegacy	29.9
Absol	Dark	SnarlBrutal SwingLegacy	29.5
Dragapult	DragonGhost	AstonishShadow Ball	28.7
Excadrill	GroundSteel	Mud SlapEarthquake	28.4
Hoopa	PsychicGhost	AstonishShadow Ball	28.2
Lunala	PsychicGhost	Shadow ClawShadow Ball	28.2
Eternatus	PoisonDragon	Dragon TailDynamax CannonLegacy	28.1
Gholdengo	SteelGhost	HexShadow Ball	28.1

Fog boosts the Ghost attacks above. Fog and Rainy boost Rotom.

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

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

Questions people ask

What is Rotom weak to in Pokémon GO?

Rotom takes 1.6 times from Ground, Ghost and Dark.

What's the best counter to Rotom?

Blacephalon with Astonish and Shadow Ball, worth 33.8 damage per second against Rotom's own defense. The full ranking is above.