Garchomp: First and foremost, Garchomp serves as this team's Stealth Rock setter, being able to set it up at least once over the course of the match most of the time, but it does much, much more than that. Outside of simply setting up Stealth Rock to make it's teammates jobs easier, it carries a threatening offensive presence of its own with its nerfed but still great dual STABs and strong 130/80/102 offenses, and also provides me with a check to some of the most important important Pokemon in the tier such as Aegislash, Heatran, Charizard Y, and Talonflame, the latter of which thanks to Rocky Helmet, which makes Talonflame practically kill itself w/ recoil simply for touching Garchomp, even if it does a lot of damage in the process. Fire Blast was chosen in the final slot simply to do some good damage to the annoyance known as Skarmory, which despite the minus special attack nature still usually takes more than enough from the move, but if you guys think another move would fit better that's okay too.
Mawile: Mega Mawile is what started the team off, and it's honestly one of my absolute favorite Pokemon to use in the metagame at the moment. It's kind of like a combination of Azumarill and Bisharp, taking good traits from both and combining them to make one damn monster of a Pokemon. Mega Mawile's base attack when taking Huge Power into account is simply incredible. For example, as mentioned in the introduction, Mega Mawile's base attack stat is so high that its Play Rough actually does more damage than Choice Band Azumarill's can muster, which is pretty damn impressive in and of itself. Along with this, its Sucker Punch and Knock Off come damn close to matching Life Orb Bisharp's in raw power. Swords Dance just adds on to this power (although it can obviously sweep even at +0 lol) and makes Mawile a force to be reckoned with, and because of Mawile's good bulk, Intimidate ability pre mega, and great Steel/Fairy typing, it's not very hard to set one up and clean house at all. The evs are standard Mawile fare, maximizing attack and aiming to outspeed min speed base 65s, the test are put into hp for some bulk.
Keldeo: The Hydro Pump nerf, fairy-type, and loss of rain might have hurt Keldeo a bit, but that doesn't mean it isn't still a good Pokemon! In fact, Keldeo is one of the most important Pokemon on this team and i don't think it'd work anywhere nearly as well without it lol. Choice Specs Keldeo is an excellent holepuncher, using its incredibly powerful Hydro Pumps and Secret Swords to heavily pressure the opposing team, especially once things like Lati@s are sufficiently weakened. As for the last two moves, i decided to choose Scald and Hidden Power Flying. Scald provides Keldeo with a more reliable but still powerful water-type STAB move to use when Hydro Pump really can't afford to miss, and it has a pretty nasty burn chance to boot, which can be an annoyance to at least some of the Pokemon aiming to switch in on it. Hidden Power Flying is used here exclusively for Mega Venusaur, who can easily wall keldeo otherwise. Aside from simply spamming attacks and threatening Heatran for Mawile, Keldeo is important simply because of the fact that it can help me out against big threats such as Bisharp, Mega Tyranitar, post mega Mega Gyarados, and Greninja (watch out for Hp Grass/Extrasensory!). Overall, as mentioned a very integeral member of this team, and i have a hard time seeing the team performing nearly as well w/o Keldeo's help.
Thundurus: Thundurus is such a great Pokemon to use on offensive teams it's not even funny, and this team is no exception. Thundurus enters the stage here as not just another powerful and fast offensive threat (although it does that excellently obviously) , but also as sort of an (oh shit!) button Pokemon that can get you out of sticky situations quite often. Thundurus's Electric/Flying typing and great Speed stat lets it serve as a check to one of the most dangerous Pokemon in the tier: Mega Pinsir, being able to take boosted quick attacks/unboosted returns and easily KOing with a super effective Thunderbolt (the flying resist doesn't hurt against Talonflame either, especially against Adamant varients that can't outspeed and Flare Blitz you). Outside of this, Thundurus's priority Thunder Wave is absolutely invaluable, stopping all kinds of offensive threats such as +1 Mega Charizard X, +1 Gyarados, +1 Mega Tyranitar, and Greninja in a pinch, although almost always at the cost on Thundurus's life. Both Leftovers and Life Orb are more than viable on Thundurus, Life Orb gives you some nice extra power, but the recovery from Leftovers gives Thundy a bit more longevity and assures you can keep Thundurus alive long enough to stop what it needs to stop.
Aegislash: Aegislash imo is probably one of the most feared Pokemon in the tier at the moment, and for good reason. Aegislash serves as this team's pivot of sorts , being able to switch into pretty much any non super effective move with ease thanks to its great typing and amazing 60/150/150 defenses, especially from things such as Lati@s, Deoxys-S, and opposing Thundurus. But unlike other Pokemon with similar levels of bulk, THE CRUMBLER doesn't just sit around, the name should speak for itself, once it switches in it can simply blast the opposing teams with nuclear Shadow Balls, crumbling pretty much anything that doesn't resist it with that move alone. As for the other two offensive moves, Sacred Sword is nice to hit both Tyranitar and Bisharp on the switch trying to take advantage on Aegislash, OHKOing both if you have good prediction skills, meanwhile Iron Head still hits Tyranitar and hits things like Clefable more consistently, but leaves you completely vulnerable to the Dark Knight. Shadow Sneak is great simply to pick things off with priority, and it's also a great weapon against lead deoxys (as long as they don't have red card) in conjunction with Shadow Ball, with the ball+sneak combo being able to limit both of them to just Stealth Rock most of the time. However, Pursuit is a great alternative, trapping things such as Lati@s, which of course makes Keldeo that much more threatening.
Deoxys-S: Offensive Deoxys-Speed rounds off this version of the team, and its probably one of the best non Talonflame revenge killers in the entire metagame. Deoxys-S is so damn fast that it doesn't even need a Choice Scarf or anything to do its job, instead outspeeding pretty much anything in the metagame easily....including relatively fast Choice Scarf users such as Garchomp. This amazing Speed, good coverage, and ability to switch moves gives Deoxys-S the ability to revenge kill a variety of threats, and also the ability to clean up teams once things like priority are removed. Hidden Power Fire was used during the Genesect metagame to get the jump on it, but now that it's banned on Pokemon showdown some alternatives are viable too, including Knock Off to do some decent damage to Aegislash on the predicted switch while removing its item.