I almost completely inherited the Archaludon + Mega Lucario face-to-face build from the M-1 era. A simple build where Archaludon sets up Stealth Rock and avoids being a target, then pushes through in direct confrontations. Final rank 751, rating 2312.
Archaludon: Sitrus Berry, max CS. Deals with Mega Florges and Mega Meganium that are entrenched with Flash Cannon, or frequently retreats. Almost always starts, an excellent Stealth Rock attacker with great Stealth Rock setup and chip damage, and target evasion capabilities.
Mega Lucario: Lucarionite, max CS, fastest (to snipe Mega Metagross). Thanks to Flash Cannon, it can deal with lines that Luster Cannon couldn't. If there are 2 or more Pokémon that resist Fighting/Steel by 2x or more, switch to Mega Gyarados.
Mega Gyarados: Gyaradosite, max AS. Very effective in this environment, highest selection rate. Waterfall → Iron Head (for Alolan Ninetales) / Crunch / Earthquake / Dragon Dance. After Mega Evolving, it resists all opponent's priority moves, making it the strongest unkillable creature.
Drednaw: Focus Sash, max AS. Water/Ghost offensive pressure, also used for switching with Aqua Jet. Avoids being selected against Meowscarada and Hisuian Samurott.
Garchomp: Choice Scarf, max AS. Only selected when it's effective or when Raichu is present.
Clefable: Leftovers, Unaware. A setup Pokémon that counters Meowscarada, Hisuian Samurott, Mimikyu, and Mega Staraptor with Cosmic Power and Flamethrower.
Archaludon + Mega Lucario (or Mega Gyarados) + Drednaw for 70-80% of battles. For the rest, Clefable instead of Drednaw.
Meowscarada (biggest natural enemy), Gengar (both Focus Sash and Mega are tricky), Mega Venusaur (too bulky and everyone uses Earth Power).