Weak toGroundElectricPsychic ×1.6

Attacker	Type	Moveset	DPS
Regieleki	Electric	Lock OnThunder CageLegacy	42.0
Mewtwo	Psychic	ConfusionPsystrikeLegacy	38.2
Zeraora	Electric	Volt SwitchPlasma Fists	36.1
Zekrom	DragonElectric	Charge BeamFusion BoltLegacy	35.3
Xurkitree	Electric	Thunder ShockDischarge	34.9
Deoxys	Psychic	Zen HeadbuttThunderbolt	33.4
Alakazam	Psychic	ConfusionPsychicLegacy	32.6
Groudon	Ground	Mud ShotPrecipice BladesLegacy	31.7
Azelf	Psychic	ConfusionFuturesight	31.6
Hoopa	PsychicGhost	ConfusionPsychic	31.5
Espeon	Psychic	ConfusionPsychic	31.5
Regigigas	Normal	Zen HeadbuttCrush GripLegacy	31.4

Rainy boosts the Electric attacks above. Overcast and Rainy boost Tentacool.

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

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

Questions people ask

What is Tentacool weak to in Pokémon GO?

Tentacool takes 1.6 times from Ground, Electric and Psychic.

What's the best counter to Tentacool?

Regieleki with Lock On and Thunder Cage, worth 42.0 damage per second against Tentacool's own defense. The full ranking is above.