Groudon @ Red Orb
Ability: Drought
EVs: 252 HP / 56 Def / 200 SpD
Relaxed Nature
- Stealth Rock
- Precipice Blades
- Overheat
- Toxic
OR
Groudon @ Red Orb
Ability: Drought
EVs: 252 SpA / 100 SpD / 156 Spe
Mild Nature
- Rock Polish
- Precipice Blades
- Fire Blast
- Hidden Power Ice
Defensive PDon can come in once on any of Dusk Mane's moves and as long as it's at nearly-full HP will live any two hits - or any one +2 hit - without fail. Overheat OHKOs Dusk Mane in return. Faster PDon variants (namely the Rock Polish sets, which generally hit 255 Speed as a bare minimum) can accomplish something relatively similar, living any unboosted hit from Dusk Mane and OHKOing it with a special Fire move or, with significant Attack investment, Precipice Blades. Accuracy can obviously prove problematic as a single miss will probably get you 6-0'd but
PDon is about as bog-standard of a Dusk Mane check as you can get, especially since it's on 99% of teams. Its presence alone is generally enough to force Dusk Mane out and as a result you can start getting spicy with your predictions; you can get Rocks up or Toxic something if you're defensive or you can blow something the fuck up if you're offensive.
If you're looking for an actual
counter to this fucking thing without relying on something extremely unorthodox that exists solely to counter this set then good luck though.
Defensive PDon Calcs:
0 SpA Groudon-Primal Overheat vs. 0 HP / 8 SpD Prism Armor Necrozma-Dusk-Mane in Harsh Sunshine: 414-487 (123.5 - 145.3%) -- guaranteed OHKO
+2 248+ Atk Necrozma-Dusk-Mane Earthquake vs. 252 HP / 56+ Def Groudon-Primal: 318-376 (78.7 - 93%) -- 37.5% chance to OHKO after Stealth Rock
248+ Atk Necrozma-Dusk-Mane Earthquake vs. 252 HP / 56+ Def Groudon-Primal: 160-190 (39.6 - 47%) -- 41% chance to 2HKO after Stealth Rock
+2 248+ Atk Necrozma-Dusk-Mane Searing Sunraze Smash vs. 252 HP / 56+ Def Groudon-Primal: 238-281 (58.9 - 69.5%) -- guaranteed 2HKO after Stealth Rock
RP Pdon Calcs:
252+ SpA Groudon-Primal Fire Blast vs. 0 HP / 8 SpD Prism Armor Necrozma-Dusk-Mane in Harsh Sunshine: 459-540 (137 - 161.1%) -- guaranteed OHKO
248+ Atk Necrozma-Dusk-Mane Earthquake vs. 0 HP / 0- Def Groudon-Primal: 204-240 (59.8 - 70.3%) -- guaranteed 2HKO after Stealth Rock
(EQ always kills at +2 and the Z-move has a notable chance to OHKO at +2 as well).