#0080 · Gen 1

Slowbro (Mega) — Best counters

Weaknesses

bug×1.60ghost×1.60grass×1.60electric×1.60dark×1.60

	Pokémon	Fast move	Charged move	Weather	Score
1	Regieleki	normalLock On	electricThunder CageELITE	Rainy · partial	10013.3
2	Gengar (Mega)	ghostLickELITE	ghostShadow Ball	Fog	9713.0
3	Sceptile (Mega)	bugFury Cutter	grassFrenzy PlantELITE	Clear · partial	9512.6
4	Absol (Mega)	darkSnarl	darkBrutal SwingELITE	Fog	8911.8
5	Banette (Mega)	ghostHex	ghostShadow Ball	Fog	8511.3
6	Kartana	grassRazor Leaf	grassLeaf Blade	Clear	8411.2
7	Blacephalon	ghostAstonish	ghostShadow Ball	Fog	8311.1
8	Manectric (Mega)	electricThunder Fang	electricWild Charge	Rainy	8211.0
9	Tyranitar (Mega)	darkBite	darkBrutal Swing	Fog	8210.9
10	Heracross (Mega)	bugStruggle Bug	bugMegahorn	Rainy	8110.8
11	Xurkitree	electricThunder Shock	electricDischarge	Rainy	8110.8
12	Pheromosa	bugBug Bite	bugBug Buzz	Rainy	8010.6
13	Houndoom (Mega)	darkSnarl	darkFoul Play	Fog	7910.5
14	Ampharos (Mega)	electricVolt Switch	electricZap Cannon	Rainy	7910.5
15	Gardevoir (Mega)	grassMagical Leaf	ghostShadow Ball	Fog · partial	7910.5
16	Zekrom	electricCharge Beam	electricFusion BoltELITE	Rainy	7810.3
17	Deoxys (Attack)	poisonPoison Jab	electricZap Cannon	Rainy · partial	7610.1
18	Shaymin (Sky)	grassMagical Leaf	grassGrass Knot	Clear	7610.1
19	Darkrai	darkSnarl	ghostShadow Ball	Fog	7510.0
20	Kyurem (Black)	ghostShadow Claw	electricFusion Bolt	Rainy · partial	749.9

Slowbro (Mega) is weak to Bug (×1.6), Ghost (×1.6), Grass (×1.6), Electric (×1.6), Dark (×1.6).
Watch its Water/Psychic/Ice/Fighting moves — counters like Gengar (Mega) and Sceptile (Mega) take super-effective damage from them.
Rainy weather boosts Electric moves ×1.2 — the best time to battle Slowbro (Mega).

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