Tbh I just wanted to show off the new shiny Volcanion online, but it turned out to be the perfect partner for Clefable so I decided to stick with the team and managed to get it to rank A. Skarmory probably isn't the best 3rd pick, but I wanted a Ground immunity to check all the Garchomps and Swamperts and I couldn't think of anything better. Electric types are a big issue for the team obviously (especially Zeraora) but they're not too common thanks to how strong Garchomp and Swampert are.
Clefable was definitely the MVP of the team. It is holding an Expert Belt and is Alpha, which I think is important to maximize the range and size of its moves. It is hypertrained and has max HP and max Sp. Atk EVs, the leftover EVs in Def. The moves are Moonblast, Meteor Beam, Focus Blast and Flamethrower. I prefer Flamethrower over Fire Blast for the shorter cooldown and longer range which makes it more consistent. Initially I was holding its mega stone, but I found myself rarely ever mega evolving it so I switched to Expert Belt once I got to about rank C. Its excellent coverage enables it to hit most of the meta super effectively. Meteor Beam is what separates Clefable from other Fairy types since most people are used to using Fire types to check Fairies such as Magearna, but Clefable pulls an UNO reverse card against them. Just be sure to try to only use it as a plus move since it has a long activation time otherwise.
Volcanion has a pretty standard build. Hypertrained, max HP and max Sp. Atk EVs, the rest in Sp. Def and it's holding an Assault Vest. The moves are Steam Eruption, Heat Wave, Focus Blast and Scorching Sands. I prefer Scorching Sands over Earth Power for the much faster activation time and high burn chance, which couples well with Steam Eruption's high burn chance. Heat Wave is the preferred Fire move since it tracks opponents. Focus Blast is Volcanion's best option against Baxcalibur and mega Garchomp Z, but it also is very handy for Dark types such as Darkrai and Mega Greninja. Its unique typing gives it a 4x resistance to Steel, which lets it easily switch into usual Clefable counters such as Metagross, Melmetal, Gholdengo, Magearna and mega Lucario Z and threaten a OHKO on most of them with Heat Wave+. Meanwhile, Clefable can switch into problematic Dragon types for Volcanion such as Garchomp, Dragonite, Baxcalibur and mega Feraligatr, although it has to be weary of regular mega Garchomp's Earthquake which does huge damage.
Skarmory was the least used by far since it's VERY dependent on mega evolving and thus the most difficult to setup safely. However, if you can achieve this it's a force to be reckoned with. The build is pretty standard: Alpha, hypertrained, max HP EVs and max Atk EVs, rest in Sp. Def and holding its mega stone. Moves are Fly, Drill Run, Sky Attack and Swords Dance. Most people prefer Steel Wing or Rock Slide instead of Sky Attack, but Steel Wing is too weak and Rock Slide is too easy to avoid by running IMO. Sky Attack is best used once mega Evolved since the activation time is significantly reduced when used as a plus move. When backed by a Swords Dance boost as well, mega Skarmory's Sky Attack OHKOs just about anything that doesn't resist it. Alpha is pretty important here to increase the range and size of Sky Attack significantly once mega evolved, it can travel across most maps entirely which is always funny to see 🤣