Counter:
Hippowdon
Hippowdon @ Leftovers
Ability: Sand Stream
EVs: 252 HP / 252 Def / 4 Spe
Impish Nature
- Earthquake
- Stealth Rock
- Slack Off
- Stone Edge
(stolen from the dex) A spread of 252 HP / 252 Def gives Hippowdon the bulk to take on Mega Pinsir and Mega Charizard X, while also walling physical attackers such as Garchomp, Excadrill, and Terrakion. Such a set is better suited for stall teams that already have a check or counter to Thundurus and other Electric-types, while being a better answer to physical attackers, such as Garchomp and Excadrill.
252 Atk Choice Band Terrakion Stone Edge vs. 252 HP / 252+ Def Hippowdon: 78-93 (18.5 - 22.1%) -- possible 6HKO after Leftovers recovery
252 Atk Choice Band Terrakion Close Combat vs. 252 HP / 252+ Def Hippowdon: 187-222 (44.5 - 52.8%) -- guaranteed 3HKO after Leftovers recovery
0 Atk Hippowdon Earthquake vs. 0 HP / 0 Def Terrakion: 260-308 (80.4 - 95.3%) -- guaranteed 2HKO (guaranteed OHKO after the Close Combat's Def drop)
Physical defensive Hippowdon is a counter to Jolly CB Terrakion because is 3HKOed by Close Combat and OHKOes back thanks to the Def drop. If Terrakion chooses another move, Terrakion isn't even a threat.