I might make a nomination of my own, but for now i'm just going to give people a point of view on what our last Pokemon is going to need to do here.
As the sixth and final slot on this team before the team is done, what we choose here and how well it performs overall could make or break this team, the team might seem solid now, but there are still some problems that i can clearly see that i think p. much need to be fixed with the final slot here. So whatever you guys nominate as the final Pokemon, take into account these threats and make sure that they can help out vs at least some of them, or at the very least not outright lose to them.
Looking through the viability rankings, here are some of the biggest threats to this team at the moment imo.
Virizion: Swords Dance Virizion with Stone Edge pretty much sweeps us here lol, of course it has to hit two stone edges against xatu and vivillon to do so, but if its able to accomplish this we simply flat out lose, Virizion can set up on choice locked lanturn and rhyperior too, so it's not like it'll never get a chance to boost.
Reuniclus and Cresselia: Yeah the bulky CM Psychic-types could end up being problematic here, We don't have a single way to hit these Pokemon super effectively, and once they end up as the last Pokemon they can simply keep on boosting and recovering until they become completely unbreakable, being able to set up on xatu pretty easily in particular. Good luck winning a CM war with vivi too, since both of them commonly run psyshock. Personally i think Megahorn>Roar on rhyperior would help out with this quite a bit, especially vs Cresselia, but we aren't supposed to be doing minor changes now.
Hp Rock Sceptile: This is uncommon but still around, same thing as Virizion pretty much except it doesnt rely on boosting as much.
Mega Abomasnow: can hit everything except Cobalion hard with at least one coverage move/Ice Shard and can switch in on lanturn pretty easily, not as big of a threat as the others, but we don't want or sixth mon outright losing to this.
We most likely won't be able to cover everything+things i missed in one slot, but just remember to keep this in mind when selecting a sixth pokemon nomination.