Gouging Fire @ Booster Energy  
Ability: Protosynthesis  
Tera Type: Fire  
EVs: 88 HP / 252 Atk / 168 Spe  
Jolly Nature  
- Flame Charge  
- Outrage  
- Flare Blitz  
- Burning Bulwark

Serperior @ Occa Berry  
Ability: Contrary  
Tera Type: Grass  
EVs: 192 Def / 64 SpD / 252 Spe  
Timid Nature  
IVs: 0 Atk  
- Leech Seed  
- Substitute  
- Protect  
- Leaf Storm

Archaludon @ Power Herb  
Ability: Sturdy  
Tera Type: Steel  
EVs: 4 HP / 252 SpA / 252 Spe  
Timid Nature  
IVs: 0 Atk  
- Electro Shot  
- Draco Meteor  
- Flash Cannon  
- Mirror Coat  

Gouging Fire 
168 speed evs with a jolly nature allows Gouging Fire to outspeed base 80s like Regidrago and Hoopa-Unbound.
88 HP allows Gouging Fire to survive one Hoopa-U psychic from modest specs. Bulky Hoopa-Unbound can survive one outrage from 252+ attack booster Gouging Fire.
252+ SpA Choice Specs Hoopa-Unbound Psychic vs. 88 HP / 0 SpD Gouging Fire: 315-372 (84.4 - 99.7%) -- guaranteed 2HKO
Flame charge gives Gouging Fire a better matchup against fast pressure stall Zapdos and bulky, but non-physically defensive, Ogerpon-Hearthflame and Wellspring. Dragon dance is an alternative to beat all Ogerpon and improve the Iron Crown matchup.
252 Atk Protosynthesis Gouging Fire Flame Charge vs. 0 HP / 0 Def Zapdos: 112-133 (34.8 - 41.4%) -- guaranteed 3HKO
252 Atk Protosynthesis Gouging Fire Outrage vs. 0 HP / 0 Def Zapdos: 268-316 (83.4 - 98.4%) -- guaranteed 2HKO 
252 Atk Protosynthesis Gouging Fire Flame Charge vs. 252 HP / 0 Def Ogerpon-Hearthflame: 114-135 (31.3 - 37%) -- 77.9% chance to 3HKO
252 Atk Protosynthesis Gouging Fire Outrage vs. 252 HP / 0 Def Ogerpon-Hearthflame: 271-319 (74.4 - 87.6%) -- guaranteed 2HKO

Serperior 
Occa berry with 192 defense evs allows Serperior to survive adamant Entei flare blitz into extreme speed. Kebia berry is an alternative to beat choice banded Donphan's gunk shot, though Serperior already has a favorable matchup via sub spam (0.8^4 = 0.4096). Speed is just max, and special defense is the chosen dump stat.
252+ Atk Entei Flare Blitz vs. 0 HP / 192 Def Occa Berry Serperior: 169-201 (58 - 69%) -- guaranteed 2HKO
252+ Atk Entei Extreme Speed vs. 0 HP / 192 Def Serperior: 76-90 (26.1 - 30.9%) -- guaranteed 4HKO
252+ SpA Archaludon Draco Meteor vs. 0 HP / 64 SpD Serperior: 220-261 (75.6 - 89.6%) -- guaranteed 2HKO
Archaludon

Archaludon
max special attack/max speed timid. Mirror coat is for Landorus-Incarnate and Raging Bolt.

Difficult matchups:
Iron Crown - 8 HP / 252 Def / 252 Spe Timid Iron Crown can iron defense on turn one against Gouging Fire and may live a flame charge into flare blitz and kill back with stored power.
252+ Atk Protosynthesis Gouging Fire Flame Charge vs. +2 8 HP / 252 Def Iron Crown: 84-102 (26 - 31.5%) -- guaranteed 4HKO
252+ Atk Protosynthesis Gouging Fire Flare Blitz vs. +2 8 HP / 252 Def Iron Crown: 204-242 (63.1 - 74.9%) -- guaranteed 2HKO
+2 0 SpA Iron Crown Stored Power (140 BP) vs. 88 HP / 0 SpD Gouging Fire: 379-447 (101.6 - 119.8%) -- guaranteed OHKO
Raging Bolt - Haban berry Raging Bolt with taunt can beat Serperior with correct play, and it can play around Archaludon's mirror coat. However, neither matchup is guaranteed.
Landorus-Incarnate - Life orb Landorus-Incarnate can OHKO Serperior with sludge wave, Gouging Fire with earth power, and Archaludon by playing around mirror coat. This matchup can be improved by giving Serperior kebia berry instead of occa berry.
Iron Valiant - Bulky encore / disable Iron Valiant can live one electro shot from Archaludon and beat it. This matchup can be improved by replacing flame charge on Gouging Fire with dragon dance, which I have been entirely successful at beating these Iron Valiants with.
Skeledirge - Custap berry earth power Skeledirge can beat Gouging Fire depending on the outrage/confusion rng. However, mirror coat Archaludon should be able to beat this Skeledirge.
Cresselia - I have beaten trick Cresselia with electro shot on Archaludon, but I do not know what the "correct" end result of that matchup is.