Considering the short season schedule, I prepared by deciding on the Mega Evolution Pokémon to adopt early and raising its completeness. I centered the team around the newly unlocked Mega Metagross and my beloved Mega Dragonite, basing it on the build of player Sigma, who achieved a momentary 1st place with the same combination, and refined it through actual practice in minor tournaments. I aimed for a flow where Hippowdon would take hits from opposing physical attackers and identify their type, then Mimikyu or Archaludon would finish them off.
Mega Metagross (Adamant nature, Ability Tough Claws/originally Clear Body, EVs HP 10, Attack 25, Sp. Atk 8, Speed 23): Psychic Fangs/Bullet Punch/Hammer Arm/Grass Knot. Originally focused on Thunder Punch and Earthquake, but I covered the weakness of being reluctant to send it out against builds with Hippowdon by adding Grass Knot. I also included Hammer Arm to counter subsequent Dark-type switches like Umbreon and Samurott, which significantly increased its selection rate.
Hippowdon (Impish nature, Item Sitrus Berry, Ability Sand Stream, EVs HP 32, Defense 22, Sp. Def 10, Speed 2): Earthquake/Slack Off/Yawn/Whirlwind. By mixing Slack Off and Whirlwind, I made opponents misjudge the presence or absence of its moves, which secured a high win rate against Baton Pass builds and Hippowdon mirrors. Speed was set to outspeed Pawmot.
Mimikyu (Adamant nature, Item Life Orb, EVs HP 29, Attack 26, Defense 11): Play Rough/Shadow Claw/Shadow Sneak/Swords Dance. Although it had the lowest selection rate, it was a deterrent card that put pressure on opponents. It originally held the spot of Kingambit, but due to frequent draws against builds with Staraptor, I switched to Mimikyu, which could neutralize Close Combat and counterattack.
Primarina (Modest nature, Item Leftovers, EVs HP 32, Defense 29, Sp. Atk 4, Sp. Def 1): Moonblast/Sparkling Aria/Aqua Jet/Encore. I reliably used it throughout the season without any adjustments or item changes. It had excellent type synergy, being strong against Fire and Ground types, which Hippowdon and Mega Metagross are weak against, and played the role of finishing off opponents with Encore when I had a numerical advantage.
Archaludon (Timid nature, Ability Stalwart, Item Choice Scarf, EVs Defense 1, Sp. Atk 32, Sp. Def 1, Speed 32): Draco Meteor/Flash Cannon/Dark Pulse/Thunderbolt. Since Mega Evolved Pokémon cannot hold a Choice Scarf by rule, a role for suppressing the top tier was needed, so it was adopted. Its strength was its ability to check Choice Scarf Meowscarada from the selection phase and the stealth of its Choice Scarf not being easily read. Combined with Hippowdon's Yawn strategy, it put Iron Defense Metagross to sleep and finished it off with Dark Pulse.
Mega Dragonite (Modest nature, Ability Multiscale, EVs HP 9, Defense 1, Sp. Atk 24, Speed 32): Draco Meteor/Air Slash/Flamethrower/Roost. Thanks to an environment with more Steel types, its role became clearer. Flamethrower was essential against Aegislash and Gholdengo, and Roost was crucial for maintaining Multiscale. However, I reflected on the increased losses due to being outsped in Dragonite mirrors, which became more common towards the end of the season, and self-evaluated that considering a Jolly nature to counter mirrors might be worthwhile.
Towards the end of the season, the combination of Mega Metagross + Hippowdon + Archaludon was selected most often. Hippowdon was used to first check whether the opponent's Archaludon had Sturdy/Stamina, and for Iron Defense Metagross types, a route was established to put them to sleep with Hippowdon's Yawn and then chip them down with Archaludon's Dark Pulse (which dealt about half damage).
Despite finishing 2nd, I personally regretted the increased losses due to being outsped in Mega Dragonite mirrors, which became more common in the latter half of the season.