Format: Legends Z-A Battle Club
This set was created specifically for Ranked Battle's Season 2, but I'm confident that it will retain relevance in later seasons. This set is for the real-time battle system and not intended for turn-based formats!

Chandelure @ Charcoal
EVs: 252 HP / 252 SpA / 4 SpD
Modest Nature
- Heat Wave
- Shadow Ball
- Fire Spin / Overheat
- Protect / Calm Mind
Having a check for Steel-types is all but necessary to surviving the current meta and I don't expect that to change as long as Xerneas remains unbanned. Chandelure's Charcoal-boosted Heat Wave can take out the rampant Metagross and Skarmory even without any additional boosts, so I opt for that as a more consistent option over more powerful options like Overheat or Fire Blast because Heat Wave spawns directly beneath the target and nearly always hits, whereas opponents can dodge area of effect or projectile moves by running out of range. Being able to attack from a bit of a distance is also helpful since getting up close to a Steel will often scare them into switching out, making Heat Wave the superior choice for surprising distracted opponents.
Shadow Ball is additional STAB and best used for opportunistically picking off Fire-resisters who are already weakened (Garchomp, Gyarados). As a bonus, it responds well to any Mystery Gift Gardevoirs you come across, though there will probably be fewer straggling along as time goes on. It also gives you the advantage against Delphox—just be aware that Delphox gets Shadow Ball too.
Fire Spin is a more niche option but I've had great experiences where it's worked really well, given the right situation, in a way that no other move could've done. A Plus-boosted Fire Spin covers a large area and lingers for a long time, so throwing one into a group of 2-3 preoccupied opponents can let you swipe all 2-3 KOs to your name as the combatants are too distracted to step out of the vortex. I've also had success with using it as a last-ditch effort just before getting KOed and managing to score a revenge kill from the grave while waiting for the respawn timer. Because you aren't able to precisely control where your Pokemon steps, a lot of people run into and kill themselves on it by accident. I'm vouching that this unusual pick is worth trying, but if you want a more straightforward offense-forward set, use this slot for Overheat instead.
Protect helps you survive and counterattack Metagross and Garchomp's Earthquake and Skarmory's Drill Run if you're directly confronted and can't hit first. You could run Calm Mind instead, but I don't think it's really as useful since Heat Wave/Overheat is already strong enough to handle your target opponents and this fast-paced format relies heavily on switching.
Why no Chandelurite? On some level, because you just don't need it... Mega Chandelure's 175 base Sp. Atk is alluring, but you can already effectively check the dominant Steels of the meta (which is the main point of this set) without it. It also isn't bulky enough to offset the larger hitbox and the extra attention it attracts, so it's hard to sweep or keep up a decent lifespan when you're effectively asking to get triple-teamed by the other players. So ironically, even though I think M-Chandelure is awesome, I don't think it's actually worthwhile in the format of the game it was introduced in and I find it more effective to save the Mega Energy for evolving a different team member or for spamming Plus moves.