#0351 · Gen 3

Castform (Rainy) — Best counters

Weaknesses

	Pokémon	Fast move	Charged move	Weather	Score
1	Regieleki	normalLock On	electricThunder CageELITE	Rainy · partial	10013.3
2	Sceptile (Mega)	grassBullet Seed	grassFrenzy PlantELITE	Clear	9112.1
3	Kartana	grassRazor Leaf	grassLeaf Blade	Clear	8411.2
4	Manectric (Mega)	electricThunder Fang	electricWild Charge	Rainy	8211.0
5	Xurkitree	electricThunder Shock	electricDischarge	Rainy	8110.8
6	Ampharos (Mega)	electricVolt Switch	electricZap Cannon	Rainy	7910.5
7	Zekrom	electricCharge Beam	electricFusion BoltELITE	Rainy	7810.3
8	Deoxys (Attack)	psychicZen Headbutt	electricZap Cannon	Rainy · partial	7710.2
9	Shaymin (Sky)	grassMagical Leaf	grassGrass Knot	Clear	7610.1
10	Venusaur (Mega)	grassVine Whip	grassFrenzy PlantELITE	Clear	749.9
11	Groudon (Primal)	groundMud Shot	grassSolar Beam	Clear	739.7
12	Thundurus (Therian)	electricVolt Switch	electricThunderbolt	Rainy	729.6
13	Roserade	grassMagical Leaf	grassLeaf Storm	Clear	719.4
14	Zarude	grassVine Whip	grassPower Whip	Clear	709.3
15	Deoxys (Normal)	electricCharge Beam	electricThunderbolt	Rainy	699.2
16	Eternatus	poisonPoison Jab	dragonDynamax CannonELITE	Windy · partial	699.2
17	Kyurem (Black)	dragonDragon Tail	electricFusion Bolt	Rainy · partial	699.1
18	Electivire	electricThunder Shock	electricWild Charge	Rainy	679.0
19	Latios (Mega)	dragonDragon Breath	grassSolar Beam	Clear · partial	679.0
20	Gallade (Mega)	psychicPsycho Cut	grassLeaf Blade	Clear · partial	678.9

Castform (Rainy) is weak to Grass (×1.6), Electric (×1.6).
Watch its Water/Normal/Electric moves — counters like Groudon (Primal) take super-effective damage from them.
Rainy weather boosts Electric moves ×1.2 — the best time to battle Castform (Rainy).

Rankings are estimated cycle DPS (attack stat × move damage ÷ cycle time, with STAB and type effectiveness). Not a full battle simulation.