Weak toFightingRockGrassElectric ×1.6

Attacker	Type	Moveset	DPS
Regieleki	Electric	Lock OnThunder CageLegacy	36.1
Lucario	FightingSteel	Force PalmAura SphereLegacy	32.3
Zeraora	Electric	Volt SwitchPlasma Fists	31.0
Kartana	GrassSteel	Razor LeafLeaf Blade	30.9
Zekrom	DragonElectric	Charge BeamFusion BoltLegacy	30.3
Xurkitree	Electric	Thunder ShockDischarge	29.9
Pheromosa	BugFighting	Low KickFocus Blast	29.6
Terrakion	RockFighting	Double KickSacred SwordLegacy	29.4
Blaziken	FireFighting	CounterAura Sphere	29.2
Breloom	GrassFighting	Force PalmGrass KnotLegacy	27.7
Glimmora	RockPoison	Rock ThrowMeteor Beam	27.4
Rampardos	Rock	Smack DownRock Slide	27.1

Rainy boosts the Electric attacks above. Rainy and Snow boost Walrein.

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

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

Questions people ask

What is Walrein weak to in Pokémon GO?

Walrein takes 1.6 times from Fighting, Rock, Grass and Electric.

What's the best counter to Walrein?

Regieleki with Lock On and Thunder Cage, worth 36.1 damage per second against Walrein's own defense. The full ranking is above.