Weak toGrassElectric ×1.6

Attacker	Type	Moveset	DPS
Regieleki	Electric	Lock OnThunder CageLegacy	58.4
Zeraora	Electric	Volt SwitchPlasma Fists	50.2
Kartana	GrassSteel	Razor LeafLeaf Blade	50.0
Zekrom	DragonElectric	Charge BeamFusion BoltLegacy	49.0
Xurkitree	Electric	Thunder ShockDischarge	48.5
Roserade	GrassPoison	Magical LeafLeaf Storm	42.6
Eternatus	PoisonDragon	Poison JabDynamax CannonLegacy	42.5
Deoxys	Psychic	Charge BeamThunderbolt	42.2
Electivire	Electric	Thunder ShockWild Charge	42.0
Zarude	DarkGrass	Vine WhipPower Whip	41.8
Rillaboom	Grass	Razor LeafFrenzy PlantLegacy	41.3
Raikou	Electric	Volt SwitchWild Charge	40.8

Rainy boosts the Electric attacks above. Rainy boosts Horsea.

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

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

Questions people ask

What is Horsea weak to in Pokémon GO?

Horsea takes 1.6 times from Grass and Electric.

What's the best counter to Horsea?

Regieleki with Lock On and Thunder Cage, worth 58.4 damage per second against Horsea's own defense. The full ranking is above.