Weak toGhostDark ×1.6

Attacker	Type	Moveset	DPS
Blacephalon	FireGhost	AstonishShadow Ball	37.6
Darkrai	Dark	SnarlShadow Ball	33.9
Chandelure	GhostFire	HexShadow Ball	33.6
Gengar	GhostPoison	LickShadow BallLegacy	33.6
Absol	Dark	SnarlBrutal SwingLegacy	32.9
Dragapult	DragonGhost	AstonishShadow Ball	32.1
Hoopa	PsychicGhost	AstonishShadow Ball	31.5
Lunala	PsychicGhost	Shadow ClawShadow Ball	31.4
Eternatus	PoisonDragon	Dragon TailDynamax CannonLegacy	31.4
Gholdengo	SteelGhost	HexShadow Ball	31.4
Zoroark	Dark	SnarlFoul Play	31.3
Chi-Yu	DarkFire	SnarlDark Pulse	31.2

Fog boosts the Ghost attacks above. Fog boosts Yamask.

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

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

Questions people ask

What is Yamask weak to in Pokémon GO?

Yamask takes 1.6 times from Ghost and Dark.

What's the best counter to Yamask?

Blacephalon with Astonish and Shadow Ball, worth 37.6 damage per second against Yamask's own defense. The full ranking is above.