Weak toGroundGhostPsychicDark ×1.6

Attacker	Type	Moveset	DPS
Mewtwo	Psychic	ConfusionPsystrikeLegacy	51.4
Blacephalon	FireGhost	AstonishShadow Ball	48.1
Alakazam	Psychic	ConfusionPsychicLegacy	43.9
Hoopa	PsychicGhost	ConfusionShadow Ball	43.6
Darkrai	Dark	SnarlShadow Ball	43.3
Chandelure	GhostFire	HexShadow Ball	43.0
Gengar	GhostPoison	LickShadow BallLegacy	42.9
Lunala	PsychicGhost	ConfusionShadow Ball	42.7
Groudon	Ground	Mud ShotPrecipice BladesLegacy	42.6
Azelf	Psychic	ConfusionFuturesight	42.5
Espeon	Psychic	ConfusionPsychic	42.3
Absol	Dark	SnarlBrutal SwingLegacy	42.0

Windy boosts the Psychic attacks above. Fog and Overcast boost Haunter.

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

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

Questions people ask

What is Haunter weak to in Pokémon GO?

Haunter takes 1.6 times from Ground, Ghost, Psychic and Dark.

What's the best counter to Haunter?

Mewtwo with Confusion and Psystrike, worth 51.4 damage per second against Haunter's own defense. The full ranking is above.