The team is centered on the Psychic/Fire Mega that newly gained Mega Evolution this season, and, drawing on previously published build information, it fixed a stable lead Pokémon and Umbreon as the core. To these three, a second Mega (Grass type) was added to cover Ghost/Water opponents that the core struggles against, along with a support that reliably lays Toxic Spikes, and a Ground type that breaks directly through stall/screen compositions, to complete the team. The win condition is either to get the Mega ace into a state where it can clean up the entire opposing team, or to slowly crush the opponent through Umbreon's Yawn-passing loop.
The usual picks are one lead Pokémon + the Mega + Umbreon as the default, and only when facing a Water-type opponent is Umbreon dropped in favor of sending out both Megas together. The lead chooses between pre-emptive Stealth Rock or an immediate attack depending on the opponent's composition, and of the two Megas covering different type matchups, whichever hits the opponent better is sent out. Failing to respond pre-emptively to a Swords-Dance-style Ground type or a stacking Rock type makes the team easy to overwhelm, so this is guarded against as the top priority.