Mega Meowstic / Espathra Psychic Terrain Gravity

Synergy

Use female Meowstic for the Competitive ability. Mega Meowstic's Trace ability lets it copy powerful abilities (Intimidate, Swift Swim, Lightning Rod) while serving as the Psychic Terrain + Expanding Force sweeper. Espathra's Speed Boost gets it to +1 so it can manually set Psychic Terrain, powering up Expanding Force. Sableye's Prankster Gravity pulls flying-types to the ground, boosts the accuracy of Hypnosis (Espathra + Milotic), Dragon Rush, and Iron Tail on Garchomp.

Win Conditions

Sableye sets Gravity while Espathra grabs a Speed Boost, then Mega Meowstic fires boosted Expanding Force under Psychic Terrain. Gravity also enables Garchomp to one-shot Charizard with Stomping Tantrum after pulling it to the ground.

Lead Options

Espathra + Sableye, Sableye + Garchomp

Threats

Dark types are strong against the Psychic spam core; Aerodactyl using Dual Wingbeat is also a threat (countered partially by Whimsicott's Coba Berry). Intimidate users can be neutered if Mega Meowstic can Trace the Intimidate for a +2 boost.