Nd mid ladder main here, interesting team (and theme) you got here. Imma try and give some suggestions based on what I know about the meta.
Meowscarada looks solid as a suicide lead, but the thing is you got Court Change Cinderace, which can basically turn all your work against you. I personally prefer Glimmora as a suicide lead due to extra hazard options, Spiky Shield for scouting, Memento for a save switch and denying hazard removal, and Mortal Spin to remove opposing hazards. Meowscarada has no way of safely bringing in its teammates after it has set down hazards, so if the opponent does not KO it, it's just left sitting around firing off Flower Tricks and Knock Offs, which gives opportunity for something like Corviknight to blow the hazards away for free. However, Meowscarada is WAY better against Mega Diancie, a formidable threat in the nd meta and something you lack answers to, so maybe it is a better fit. I will try and provide better Diancie checks in this answer though.
Gardevoir is a risky pick, as it loses outright if slightly chipped to one of the best megas, Scizor, while fearing Zard Y as well if chipped. It also fears revenge killing from Mega Lopunny, while being bombarded all around by Dragapult, Heatran, and Kartana, notably being walled by Heatran, which your team seems to have trouble breaking through. I'll get back to this Pokemon later.
Braviary-H is not good. It's slow, it's not strong by offensive standards, and while it does provide support, other Pokemon can do it better. I'll throw Kingdra in here as well, as your whole idea of setting up with Kingdra supported by Braviary is quite flawed. Tailwind only lasts four turns, and because it takes on turn to get Kingdra onto the field, it effectively only has three turns. Getting up Focus Energy takes another turn, and by then the opponent would have already switched in a defensive counter, such as Specially Defensive Pex. All it takes now is one Toxic and this strategy is screwed. Getting Braviary in and getting a free turn for Tailwind is already quite the task, especially because this build lacks recovery. It is a good gimmick to use against your friends, and it can be...not wholly underwhelming against teams without many defensive checks, but 95 special attack and a reliance on crits makes this paring underwhelming. Again, I'll get back to this pair later.
On a brighter note, Cinderace is decent if Court Change is removed. Instead, go for something like Sucker Punch for general revenge killing utility.
Aaaand back to the dark side. As of writing this answer, Kingambit has KingamBIT the dust in NDOU, rising spiritually to the realm of NDUbers. This may be sad news, but hey, one less offensive check to your mega gardevoir. Speaking of Gard, if you're using it to break offensively early game, I suggest four attacks, dropping Calm Mind for Focus Blast in order to at least hit Heatran, as even a SpDef Heatran gets 2HKOed by Focus Blast (58-68%).
As for the Kingdra-Braviary duo, I'm afraid I have no idea how to make Kingdra work, however, Braviary has...slight potential with a bulky setup variation. If you want to win, though, it is recommended that you consider one of these suggestions:
Stick to the HO theme fully. I'm talking no defense, full throttle ahead. Scarf Lele for early game breaking, revenge killing, and protecting against bullet punch to help Gard. Add in a Psychic Seed Sneaseler or SD Garchomp to hit Heatran and other Steels, then round the team off with a QD Volcarona, who, along with Cinderace, can prey on a team after Heatran is dispatched. In all honesty, I don't know if these Pokemon work together well (I came up with them on the spot) but the general idea is to throw in setup sweepers and choiced attackers and try to synergize their typings and offensive matchups. However, if you want me to recommend specific Pokemon tailored for your team, or you want to synergize Pokemon with your favorites, let me know and I will gladly spend the time to help.
Play more defensively, and shift into a more Balanced Offensive team. Mega Gard is something you commonly see on slower teams, and so a balance offensive team can still generate power without turning the game into a stallfest. For example, Scarf Gholdengo can help maintain Spikes while threatening removers such as Tusk and Corv with fast attacks and trick. Lando-T is a versatile member that you can make either offensive or defensive, but its main role is an offensive pivot that can safely remove Heatran. Finally, your choice of a final sweeper: maybe Volc, maybe DD Pult or Bax, maybe Iron Press Zamazenta. Play around with these options and see what you like using the most.
I'm not the best at NatDex, but I hope these suggestions give you a general idea of what's good on your team and what's not. If you want, I could shift some of these Pokemon around to align with your favorites, in case you still want to maintain a theme of some sorts. Either way, enjoy beating your friends! (I know I did (and still do))
