Meloetta (P) w/ Life Orb
Serene Grace
252 Atk, 252 Spd, 4 HP
Adamant (+Atk, -SAtk)/Jolly (+Spd, -SAtk)
-Relic Song
-Drain Punch/Close Combat
-Ice Punch
-U-Turn/Return/Quick Attack
Sorry if this has been posted already. Pirouette Forme can be a great sweeper with its Attack and Speed. Because it is so fast, Adamant is a good nature to give it more power, as what outspeeds it (outside of Über) won't do much. Also, without a speed boosting nature, Aria Forme is much slower, making it possible that Meloetta will attack second when Relic Song. However, Aria Forme is bulkier, at least specially, allowing it to take a hit better.
Ghosts are a good counter as they "spinblock" and prevent Relic Song from being used, making this set useless.

This is much harder to do on one's phone...