Hybrid Fighting/Darkness build pairing Mega Lucario ex's burst damage with Igglybuff's Sleepy Lullaby and Darkrai's Bad Dreams chip pressure.

Riolu
Igglybuff
Mega Lucario ex
Darkrai
Copycat
Professor’s Research
Cyrus
Sabrina
Korrina
Poké Ball
X Speed
Arena of Antiquity
Source decklists referenced for this guide:
Open Riolu and Igglybuff, attach Fighting energy and dig for Korrina. Use Sleepy Lullaby to put the opponent to Sleep, bench Darkrai for passive 20 damage every end of turn, then evolve into Mega Lucario ex for heavy Fighting Pulse swings boosted by Korrina + Arena of Antiquity. Sabrina forces awkward switches and Cyrus pulls damaged threats for the knockout. Detailed matchup data will be updated as the format develops.
Main attacker — Fighting Pulse hits 90+ damage with an extra Fighting energy.
Disruption — Sleepy Lullaby puts the opponent's active Pokémon to Sleep.
Chip damage — Bad Dreams adds 20 damage to sleeping Pokémon at the end of each turn.
Boosts Fighting attackers by +30 damage against ex Pokémon.
Stadium — attacks against ex Pokémon do an extra 20 damage.
Bench Riolu, Igglybuff and Darkrai, attach Fighting energy and chain draw Supporters for tempo.
Use Sleepy Lullaby + Bad Dreams chip damage while Mega Evolving into Mega Lucario ex on the bench.
Close with Korrina-boosted Fighting Pulse + Cyrus, using Arena of Antiquity to seal OHKOs against ex Pokémon.