Gastrodon @ Heavy-Duty Boots
Ability: Sticky Hold
EVs: 252 HP / 4 Def / 252 SpD
Sassy Nature
- Scald
- Earthquake
- Recover
- Clear Smog/Toxic
252 SpA Choice Specs Blacephalon Shadow Ball vs. 252 HP / 252+ SpD Gastrodon: 178-211 (41.7 - 49.5%) -- guaranteed 3HKO
252 SpA Choice Specs Blacephalon Flamethrower vs. 252 HP / 252+ SpD Gastrodon: 101-119 (23.7 - 27.9%) -- 87.6% chance to 4HKO
252 SpA Choice Specs Blacephalon Overheat vs. 252 HP / 252+ SpD Gastrodon: 145-171 (34 - 40.1%) -- guaranteed 3HKO
0 SpA Gastrodon Scald vs. 0 HP / 4 SpD Blacephalon: 194-230 (78.5 - 93.1%) -- guaranteed 2HKO
0 Atk Gastrodon Earthquake vs. 0 HP / 0 Def Blacephalon: 306-362 (123.8 - 146.5%) -- guaranteed OHKO
Gastrodon is possibly the closest Pokemon that could be considered a counter to Blacephalon. This is thanks to Sticky Hold, which means unlike Blissey or Chansey, it doesn't have to worry about being crippled by Trick. Max SpDef investment means that outside of a critical hit Shadow Ball or a 20% SpDef drop, Specs Shadow Ball doesn't 2HKO Gastrodon. Earthquake is a clean OHKO on Blacephalon, whereas Scald needs some chip to kill. Heavy-Duty Boots were chosen over Leftovers so that Gastrodon doesn't have to worry about hazards damaging it.
Therefore, Gastrodon is a Hard Check/Soft Counter (not too sure) to Specs Blacephalon
Counter, accounting for the SpDef drop (when it's only 20%) or a crit isn't really fair.