The cycle build of Hippowdon + Mega Scizor that I used in the previous season M-A was directly utilized, seeing the M-B rule change as a tailwind. The previous build was inherited up to Scizor as the core, Hippowdon supporting with Stealth Rock, Hydreigon deploying from Scizor's U-turn, Mega Dragonite as a supplementary sub, and Greninja assisting Dragonite with Toxic Spikes. To solve the problem of frequent draws due to Toxic Spikes + Dragonite alone not being able to break down all stall teams, Gholdengo, newly added, was adopted as the sixth member. Final rank 43, rating 2505.
Mega Scizor: Item Scizorite, HB (2-hit resistance to Garchomp's Earthquake in non-Mega state) distribution with attack as high as possible. It acts as a cushion, bringing in advantageous attackers with delayed U-turn, then switches to a Swords Dance + Bullet Punch sweeper. It was greatly favored by the meta against Metagross and Mawile, and while somewhat disadvantaged against Blaziken and Staraptor, their low usage rate made it not a problem. Moves are Bullet Punch/U-turn/Swords Dance/Roost.
Hipowdon: Item Sitrus Berry, HD specialized to withstand a single hit from Mega Charizard Y. It's an early-game Stealth Rock setter and its ability to clear rain from rain teams is also a strength. Moves are Stealth Rock/Earthquake/Yawn/Whirlwind (countermeasure against Substitute in the air).
Hydreigon: Item Choice Scarf, CS specialized ace. Adopted as a special attacker as Scizor induces physical walls, it had good synergy as it was advantageous against Basculegion and Rotom, which Hippowdon + Scizor find troublesome, and against Delphox, which is difficult for both Megas. Being able to hit Metagross with a super effective move from above was the biggest tailwind in M-B. Moves are Draco Meteor/Dark Pulse/Flamethrower/U-turn.
Mega Dragonite
Greninja: Item Focus Sash (action guarantee), CS specialized. A Toxic Spikes setter for Mega Dragonite and a fast attacker. Moves are Toxic Spikes/Sludge Wave (fairy awareness)/Ice Beam (dragon awareness)/Mud Shot (Duraludon/Mawile awareness).
Gholdengo: Item Life Orb, HCD distribution (HD for 2-hit resistance to Primarina's Sparkling Aria, C for 11n to deal with Toxapex with Shadow Ball + 2 Special Attack boosts Shadow Ball, S for +2 speed to outspeed neutral Primarina). Its greatest strength is its ability to nullify annoying moves with its Good as Gold ability, allowing it to set up and attack for a breakdown, and its bulk makes it suitable for basic leads. It also provides burst damage with Make It Rain. It has good type synergy with Dragonite and Hydreigon and is strong against Staraptor. Moves are Shadow Ball/Make It Rain/Nasty Plot/Recover.
The basic lead is Hippowdon + Scizor + attacker: Set up Stealth Rock and attack with U-turn + attacker, aiming for one side to break through. Both Dragonite and Scizor can be used in non-Mega forms, so 2-Mega leads were also frequent. Greninja + Mega Dragonite (+ reserve 1) was a lead against compositions where Toxic Spikes and Dragonite are effective, mainly those including Corviknight, accompanied by Hippowdon (switch deterrence) or Scizor (Triple Axel receiver). Otherwise, it was operated as a face-to-face cycle.