Weak toGrass ×2.56FightingGroundElectric ×1.6

Attacker	Type	Moveset	DPS
Kartana	GrassSteel	Razor LeafLeaf Blade	43.7
Xurkitree	Electric	Thunder ShockPower Whip	37.5
Roserade	GrassPoison	Magical LeafLeaf Storm	37.3
Zarude	DarkGrass	Vine WhipPower Whip	36.5
Rillaboom	Grass	Razor LeafFrenzy PlantLegacy	36.1
Breloom	GrassFighting	Force PalmGrass KnotLegacy	35.5
Meowscarada	GrassDark	LeafageFrenzy PlantLegacy	35.3
Decidueye	GrassGhost	Magical LeafFrenzy PlantLegacy	34.7
Tapu Bulu	GrassFairy	Bullet SeedGrass Knot	34.6
Tsareena	Grass	Magical LeafGrass Knot	34.1
Sceptile	Grass	Bullet SeedFrenzy PlantLegacy	33.9
Ogerpon	Grass	Magical LeafGrass Knot	33.7

Clear boosts the Grass attacks above. Partly cloudy and Rainy boost Omastar.

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

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

Questions people ask

What is Omastar weak to in Pokémon GO?

Omastar takes 2.56 times damage from Grass, and 1.6 times from Fighting, Ground and Electric.

What's the best counter to Omastar?

Kartana with Razor Leaf and Leaf Blade, worth 43.7 damage per second against Omastar's own defense. The full ranking is above.