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Azumarill @ Assault Vest
Ability: Huge Power
EVs: 240 HP / 252 Atk / 16 SpD
Adamant Nature
- Play Rough
- Waterfall
- Aqua Jet
- Knock Off
As one of the few solid counters to Hydreigon, Azumarill is immune to Hydreigon's most spamable STAB, Draco Meteor, and resists Dark Pulse, Fire Blast, and Superpower, taking minimal damage from said coverage moves. It does take neutral damage from Flash Cannon, however, it's not STAB and isn't too strong, and fails to 3HKO after Stealth Rock damage. Azumarill easily OHKOs Hydreigon in return with Play Rough, even with an Assault Vest.
252+ SpA Life Orb Hydreigon Flash Cannon vs. 240 HP / 16 SpD Assault Vest Azumarill: 95-113 (23.6 - 28.1%) -- 91.5% chance to 4HKO
252+ SpA Life Orb Hydreigon Dark Pulse vs. 240 HP / 16 SpD Assault Vest Azumarill: 70-84 (17.4 - 20.9%) -- possible 5HKO
4 Atk Life Orb Hydreigon Superpower vs. 240 HP / 0 Def Azumarill: 70-83 (17.4 - 20.6%) -- possible 5HKO
252+ SpA Life Orb Hydreigon Fire Blast vs. 240 HP / 16 SpD Assault Vest Azumarill: 65-77 (16.2 - 19.2%) -- possible 6HKO
Mild:
252+ Atk Huge Power Azumarill Play Rough vs. 0 HP / 0- Def Hydreigon: 868-1024 (267 - 315%) -- guaranteed OHKO
Modest:
252+ Atk Huge Power Azumarill Play Rough vs. 0 HP / 0 Def Hydreigon: 780-924 (240 - 284.3%) -- guaranteed OHKO
As long as rocks aren't up, Porygon2 switches in on Fire Blast/Dark Pulse and has enough bulk to win after using T-Wave. Worst comes to worst, it can take the combination a Superpower and a Draco Meteor consecutively as long as both aren't max rolls. P2 paralyzes the Hydreigon after switching in, and recovers more damage than it takes. Three Ice Beams are guaranteed to take out Hydreigon once P2 has recovered a necessary amount of HP.
At 0:
0 Atk Life Orb Hydreigon Superpower vs. 248 HP / 204 Def Eviolite Porygon2: 138-164 (36.9 - 43.9%) -- guaranteed 3HKO
252+ SpA Life Orb Hydreigon Draco Meteor vs. 248 HP / 56+ SpD Eviolite Porygon2: 175-208 (46.9 - 55.7%) -- 77.7% chance to 2HKO
252+ SpA Life Orb Hydreigon Dark Pulse vs. 248 HP / 56+ SpD Eviolite Porygon2: 109-129 (29.2 - 34.5%) -- 4.1% chance to 3HKO
At -1/-2:
-1 0 Atk Life Orb Hydreigon Superpower vs. 248 HP / 204 Def Eviolite Porygon2: 94-112 (25.2 - 30%) -- guaranteed 4HKO
-2 252+ SpA Life Orb Hydreigon Draco Meteor vs. 248 HP / 56+ SpD Eviolite Porygon2: 87-105 (23.3 - 28.1%) -- 88.6% chance to 4HKO
-2 252+ SpA Life Orb Hydreigon Dark Pulse vs. 248 HP / 56+ SpD Eviolite Porygon2: 55-66 (14.7 - 17.6%) -- possible 6HKO
0 SpA Porygon2 Ice Beam vs. 0 HP / 0 SpD Hydreigon: 148-176 (45.5 - 54.1%) -- 45.7% chance to 2HKO
Conkeldurr @ Assault Vest
Ability: Guts
EVs: 252 Atk / 236 SpD / 20 Spe
Adamant Nature
- Drain Punch
- Mach Punch
- Ice Punch / Knock Off
- Poison Jab / Stone Edge
Assault Vest Conkeldurr can take a Draco Meteor from Hydreigon, and retaliate back with Drain Punch, healing the damage that Draco Meteor did. If Drain Punch does not OHKO, then Conkeldurr can simply pick it off with Mach Punch.
252+ SpA Life Orb Hydreigon Draco Meteor vs. 0 HP / 236 SpD Assault Vest Conkeldurr: 208-246 (59.2 - 70%) -- guaranteed 2HKO
252+ SpA Life Orb Hydreigon Fire Blast vs. 0 HP / 236 SpD Assault Vest Conkeldurr: 117-139 (33.3 - 39.6%) -- guaranteed 3HKO
252+ SpA Life Orb Hydreigon Flash Cannon vs. 0 HP / 236 SpD Assault Vest Conkeldurr: 86-101 (24.5 - 28.7%) -- 99.4% chance to 4HKO
252+ SpA Life Orb Hydreigon Dark Pulse vs. 0 HP / 236 SpD Assault Vest Conkeldurr: 64-75 (18.2 - 21.3%) -- possible 5HKO
252+ Atk Conkeldurr Drain Punch vs. 0 HP / 4 Def Hydreigon: 308-366 (94.7 - 112.6%) -- 68.8% chance to OHKO
252+ Atk Conkeldurr Mach Punch vs. 0 HP / 4 Def Hydreigon: 168-198 (51.6 - 60.9%) -- guaranteed 2HKO
Cobalion @ Leftovers
Ability: Justified
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Close Combat
- Iron Head
- Swords Dance
- Substitute
Cobalion resists both STABs and flash cannon, and can switch into any of Hydreigon's moves bar fire blast (even superpower only 2HKOs), can then proceed to outspeed and KO with close combat. Can also use the ability to force Hydreigon out to set up a SD or a sub.
252 Atk Cobalion Close Combat vs. 0 HP / 0- Def Hydreigon: 372-438 (114.4 - 134.7%) -- guaranteed OHKO
252+ SpA Life Orb Hydreigon Draco Meteor vs. 0 HP / 0 SpD Cobalion: 192-227 (59.4 - 70.2%) -- guaranteed 2HKO after Leftovers recovery
4 Atk Life Orb Hydreigon Superpower vs. 0 HP / 4 Def Cobalion: 190-224 (58.8 - 69.3%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Life Orb Hydreigon Fire Blast vs. 0 HP / 0 SpD Cobalion: 437-515 (135.2 - 159.4%) -- guaranteed OHKO
Altaria @ Altarianite
Ability: Cloud Nine / Natural Cure
EVs: 248 HP / 136 Def / 96 SpD / 28 Spe
Impish Nature
- Dragon Dance
- Roost
- Return
- Heal Bell / Substitute / Earthquake
Role: Check
King DDD is here to threaten Kirby Hydreigon by taking its attacks, even able to avoid the OHKO from Flash Cannon after Stealth Rock before Mega Evolving, and it resists or is immune to everything else. I don't think I have to tell you that Return is an OHKO, but I will anyway. It is, however, held back by its lower Speed, preventing it from being a true counter.
252+ SpA Life Orb Hydreigon Dark Pulse vs. 248 HP / 96 SpD Mega Altaria: 79-94 (22.3 - 26.6%) -- 28.9% chance to 4HKO
252+ SpA Life Orb Hydreigon Flash Cannon vs. 248 HP / 96 SpD Mega Altaria: 213-252 (60.3 - 71.3%) -- guaranteed 2HKO
4 Atk Life Orb Hydreigon Superpower vs. 248 HP / 136+ Def Mega Altaria: 44-52 (12.4 - 14.7%) -- possible 7HKO
252+ SpA Life Orb Hydreigon Fire Blast vs. 248 HP / 96 SpD Mega Altaria: 73-86 (20.6 - 24.3%) -- guaranteed 5HKO
0 Atk Pixilate Mega Altaria Return vs. 0 HP / 0- Def Hydreigon: 756-892 (232.6 - 274.4%) -- guaranteed OHKO
Terrakion @ Life Orb
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Close Combat
- Stone Edge
- Swords Dance
- Rock Polish / Substitute
Terrakion can switch in on Dark Pulse or Fire Blast, then OHKO Hydreigon with Close Combat. It can survive one Flash Cannon, but then Terrakion is vulnerable to being revenge killed.
Offensive:
252 Atk Life Orb Terrakion Close Combat vs. 0 HP / 4 Def Hydreigon: 549-650 (168.9 - 200%) -- guaranteed OHKO
252 Atk Life Orb Terrakion Stone Edge vs. 0 HP / 4 Def Hydreigon: 231-273 (71 - 84%) -- guaranteed 2HKO
+1 252 Atk Life Orb Terrakion Stone Edge vs. 0 HP / 4 Def Hydreigon: 344-407 (105.8 - 125.2%) -- guaranteed OHKO
252 Atk Life Orb Terrakion Close Combat vs. 0 HP / 4- Def Hydreigon: 616-725 (189.5 - 223%) -- guaranteed OHKO
252 Atk Life Orb Terrakion Stone Edge vs. 0 HP / 4- Def Hydreigon: 255-302 (78.4 - 92.9%) -- guaranteed 2HKO
+1 252 Atk Life Orb Terrakion Stone Edge vs. 0 HP / 4- Def Hydreigon: 383-452 (117.8 - 139%) -- guaranteed OHKO
Defensive:
252+ SpA Life Orb Hydreigon Draco Meteor vs. 0 HP / 4 SpD Terrakion: 320-378 (99 - 117%) -- 93.8% chance to OHKO
252+ SpA Life Orb Hydreigon Dark Pulse vs. 0 HP / 4 SpD Terrakion: 99-117 (30.6 - 36.2%) -- 47.7% chance to 3HKO
252+ SpA Life Orb Hydreigon Flash Cannon vs. 0 HP / 4 SpD Terrakion: 265-312 (82 - 96.5%) -- guaranteed 2HKO
252+ SpA Life Orb Hydreigon Fire Blast vs. 0 HP / 4 SpD Terrakion in Harsh Sunshine: 135-160 (41.7 - 49.5%) -- guaranteed 3HKO
0 Atk Life Orb Hydreigon Superpower vs. 0 HP / 0 Def Terrakion: 255-302 (78.9 - 93.4%) -- guaranteed 2HKO
Chansey @ Eviolite
Ability: Natural Cure
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Toxic / Thunder Wave
- Soft-Boiled
- Seismic Toss
- Heal Bell
Chansey avoids the 2HKO from any of Hydreigon's moves, even a Super Effective LO-boosted Superpower when Stealth Rock is up. Chansey can then heal itself with Soft-boiled while waiting for Hydreigon to wer itself down with the LO recoil. It can also wear Hydreigon down with Seismic Toss or cripple Hydreigon with status.
4 Atk Life Orb Hydreigon Superpower vs. 252 HP / 252+ Def Eviolite Chansey: 309-367 (43.8 - 52.1%) -- guaranteed 3HKO after Stealth Rock
252+ SpA Life Orb Hydreigon Dark Pulse vs. 252 HP / 4 SpD Eviolite Chansey: 117-138 (16.6 - 19.6%) -- possible 5HKO after Stealth Rock
252+ SpA Life Orb Hydreigon Draco Meteor vs. 252 HP / 4 SpD Eviolite Chansey: 188-224 (26.7 - 31.8%) -- possible 7HKO after Stealth Rock
Chansey Seismic Toss vs. 0 HP Hydreigon: 100-100 (30.7 - 30.7%) -- guaranteed 4HKO
Breloom @ Life Orb
Ability: Technician
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Spore
- Bullet Seed
- Mach Punch
- Swords Dance
Breloom can survive any hit except draco meteor or fire blast (if he runs that) and solidly OHKOs with Mach Punch. Breloom will be unable to live a majority of Hydreigon's moves, or live any of them at a healthy percents, so he's a decent check.
Mandibuzz (F) @ Leftovers
Ability: Overcoat
EVs: 248 HP / 252 SpD / 20 Spe
Calm Nature / Careful Nature
- Foul Play
- Roost
- Taunt / Knock Off
- Toxic / Defog
If Stealth Rocks aren't up, SpD Mandibuzz can take 2 Draco Meteors, or a Fire Blast followed by a Draco Meteor, from full and proceed to stall Hydreigon out.
252+ SpA Life Orb Hydreigon Draco Meteor vs. 248 HP / 240+ SpD Mandibuzz: 222-263 (52.4 - 62.1%) -- 98.8% chance to 2HKO after Leftovers recovery
252+ SpA Life Orb Hydreigon Fire Blast vs. 248 HP / 240+ SpD Mandibuzz: 125-148 (29.5 - 34.9%) -- 100% chance to 4HKO after Leftovers recovery
-2 252+ SpA Life Orb Hydreigon Draco Meteor vs. 248 HP / 240+ SpD Mandibuzz: 110-133 (26 - 31.4%) -- 11.5% chance to 4HKO after Leftovers recovery
With hazards off the field, Venusaur avoids the 2HKO from 2x Draco Meteor and any coverage move + Draco Meteor, and can then stall Hydreigon out with Synthesis. With Rocks it's much less certain, plus Venusaur will typically be taking up to 70% from Rocks + Draco, and won't recover it all before being forced out by something else. Then it certainly can't counter Hydreigon any more.
Charizard-Mega-Y @ Charizardite Y
Ability: Blaze
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Fire Blast
- Solar Beam
- Focus Blast
- Roost
On paper Water beats Fire, but in this case the opposite is true. Thanks to Drought, Charizard-Y crushes Gastrodon, being able to switch in on any attack, ignore Scald's burn chance, and obliterate it with Solar Beam.
0 SpA Gastrodon Scald vs. 0 HP / 0 SpD Mega Charizard Y in Sun: 68-84 (22.8 - 28.2%) -- 78.2% chance to 4HKO
252 SpA Mega Charizard Y Solar Beam vs. 200 HP / 56+ SpD Gastrodon: 612-720 (148.1 - 174.3%) -- guaranteed OHKO
and just for fun...
252 SpA Mega Charizard Y Fire Blast vs. 200 HP / 56+ SpD Gastrodon in Sun: 156-185 (37.7 - 44.7%) -- guaranteed 3HKO after Leftovers recovery
Yay a Grass type, how original. I'm going to call Celebi a counter for a few reasons; 1: Even if you're a Physical Celebi set or any other set, you can simply switch out and recover from the status infection like Scald burns or from Toxic. 2: You resist Water and Ground being a Grass type, and because you're a grass type Gastrodon will fear any attack from Celebi so it will most likely switch out. The moveset can be changed, but I chose this one for an example.