Volcarona is a fearsome sweeper once certain conditions have been met. This team is based around Volcarona being my main late-game sweeper, with the rest of the team being built around facilitating the sweep whilst also being strong wincons in their own right.
Volcarona being the MVP of choice I went with a rather standard set for the other teammates to fill in the gaps. One quiver dance is usually all it takes to clean up late-game as long as fire blast doesn't miss. Lum berry and giga drain improve the match-up against stall, avoiding stray toxics from the likes of Hippowdon while you 2HKO and getting the OHKO on Quagsire even unboosted. Burn immunity is also nice for an offensive team. Speed EVs are to outspeed scarf Lando-T after a QD and the rest into HP for a bit more longevity.
Mega Altaria is a really versatile mon and I wanted to make sure to use her in a way to benefit Volcarona. This Volc is walled by fire and dragon types, so the standard offensive DD set allows Alt to take out the majority of the problem mons such as Heatran, Dragonite, Latis, etc. In return, Volc takes care of the steels which Altaria can't touch such as Skarmory with fire blast. Between them there's not much they can't handle.
Thundurus brings an answer to Talonflame, which walls the core. With nasty plot he is also a decent wall/stallbreaker. Prankster thunder wave can be really clutch vs offence as despite having 2 forms of priority the team is relatively slow before setting up. Originally I had sludge wave to beat unaware Clefable, but Lucario can handle it and HP ice is much better coverage. Also having ice spam on 3 team members has been clutch in a few matches to help wear down the opposition.
Mamoswine brings priority to the table plus stealth rocks and an electric immunity. He is actually a great rocks setter as he threatens and can force out two of the other main rock setters in Lando-T and Chomp, helping to keep rocks off the field for Volcarona. Ice shard helps vs scarfed mons and with his STABs and thick fat can beat threats such as M-Mane, Thundurus, Hippowdon, etc. 29 HP IVs hits a life orb number.
Starmie obviously brings reliable much-needed hazard removal to the team without sacrificing offensive presence. A powerful hydro pump (can you tell I hate grounds yet?) plus psyshock to dent M-Venu and thunderbolt which, in addition to Starmie's water resist, helps vs bulky waters such as Suicune, Slowbro and Manaphy (watch out for e-ball though).
Lucario fulfils a lot of roles here, strong priority to improve the matchup vs offence, fairy killer, quad rock resist, dark absorber, toxic immunity. It's a bit of an unorthodox set, originally I went with a SD set but I felt I needed all 4 moveslots, and with a choice band Lucario is a surprisingly effective wallbreaker / late-game cleaner, especially if he can nab a justified boost. Band also guarantees the OHKO on the likes of Clefable, M-Alt etc. Not being able to switch moves sucks sometimes but I have enough sweepers and CB close combat is just stupidly powerful and definitely makes up for it on this team. As my only rock resist, ice punch is required to threaten the many ice-weak mons which carry EdgeQuake coverage. Jolly over adamant to ensure outspeeding all Altaria and the drop in power doesn't seem to matter.