This is a transition team, from Gen6 to Gen7. I decided to use the newest toy we got in OU for it, Volcanion. Maybe it's a short lived fad, but it's a really fun team. Feel free to suggest changes you see fit so it could perform potentially better. I will improve it with what Gen7's going to offer, if anything.
Teambuilding Process
It goes as follows
Volcanion is the team's star. By virtue of its fantastic typing and amazing ability, he acts as a burn-absorbing, a wall against all Water-types and a counter to a slew of important threats in OU such as Sableye-mega, Azumarill, Scizor-mega and Talonflame among others. Most importantly, though, Volcanion has unparalleled wallbreaking potential, thanks to having extremely high powered attacks, an impressive signature move and colourful coverage.
Metagross complements Volcanion extremely well. They nurture synrergy mutually, with Volcanion forcing Water-types out of the way and destroying all Steel-, Ground- and most Dark-types and Metagross-mega taking out troublesome Dragon- and Rock-types all while displaying monstrous power thanks to his ability. Finally, being a physical attacker means he gets past Special walls such as Chansey fortunately with relative ease.
Landorus-therian was a natural pick. He acts as a check to Excadrill mainly, who otherwise beats the offensive core singlehandedly, but equally beats Pinsir-Mega, Charizard-Mega-X, Lopunny-Mega, Tyranitar and more Pokemon lacking Ice-type coverage. Finally, he acts as a bulky pivot that provides Stealth Rock support.
Most of you know the roll now. I cannot make a team without Rotom-Wash. Having a washing machine on my team apparently is a morale boost on its own. This comes down to many reasons: It can complete a slow VoltTurn core with Landorus-Therian, which is crucial to bring in my attackers safely. Besides, its impressive typing and access to Pain Split and Will-O-Wisp, nifty tools that screw over my opponents, all contribute to its popularity.
At this point, the team had an interesting tendency to distribute status conditions through Volcanion's Steam Eruption and Rotom-Wash's Will-O-Wisp. Adding a way to paralyze foes and put them to sleep looked sound to me. Amoonguss was therefore a sensible choice for the team's welfare: it completed a FWG core with Volcanion and Rotom-Wash, can spread various nasty conditions, can take on relatively strong unboosted attackers such as Garchomp and Excadrill and has Regenerator, which turned it into an interesting bulky pivot.
Latios rounds the team quite well. He acts as a defog user, a revenge killer and can fire powerful attacks. Really, there is not much to be said of Latios, he's more of a glue in the team than anything but his Defogging services are always welcome, and so are the powerful attacks he can fire. Finally, Latios beats Venusaur-mega, which albeit uncommon can wall most of the team alone. However, he stacks Dark- and Ghost-weakness.
In Details
Volcanion 
| .steampowered | Volcanion |
Water Absorb | EVs: 68 HP / 252 SpA / 188 Spe
Modest Nature | IV: 0 Atk | Special Tank
Fire Blast | Steam Eruption | Sludge Wave | Earth Power
Volcanion shreds defensive cores and stall apart by virtue of his powerful attacks. Steam Eruption is the main selling point of the set, nuking everything that does not specially resist it. It also comes with high power, a high burn chance and little to no drawbacks. Fire Blast is the Fire-type STAB which Volcanion can roast Steel-, Grass- and Ice-types with it, hitting Ferrothorn, Weavile and Tangrowth most notably. Sludge Wave deals high damage to Fairy-types such as Altaria-Mega which otherwise resists the two former attacks. Finally, Earth Power is a filler move mainly, used to deal with adversary Volcanion and Heatran although its teammates are generally the ones to take care of this. The speed EVs will speedcreep all defensive Landorus-Therian, but also the other Volcanions.
Metagross-Mega 
| .titaniumripper | Metagross-Mega |
Clear Body --> Tough Claws | EVs: 4 SpD / 252 Atk / 252 Spe
Jolly Nature | IV: All 31 | Physical Sweeper
Meteor Mash | Bullet Punch | Hammer Arm | Ice Punch
What Metagross lacks in sheer power next to Volcanion, it more than makes up for it with its high speed. Thanks to Meteor Mash and Bullet Punch, Metagross can finish off a slew of foes who would otherwise switch in and take the hits, such as Sableye-mega and Latias. Hammer Arm adds much-needed coverage to beat the other Steel-types but also to take care of the likes of Bisharp, Tyranitar, a weakened Rotom-Wash and Excadrill. Finally, Ice Punch beats Landorus-Therian, Garchomp and Dragonite who would otherwise be able to take a hit.
Landorus-Therian 
| .earthshatter | Landorus-Therian|
Intimidate | EVs: 248 HP / 232 Def / 8 SpD / 20 Spe
Impish Nature | IV: All 31 | SR setter, Bulky Pivot
Stealth Rock | Earthquake | Stone Edge | U-Turn
Intimidate support and mindgames allows Landorus-therian, with Rotom-Wash's help, to soften the enemy's offensive forces to the point that they deal little damage. Stealth Rock keeps Talonflame, Charizard, Volcarona, Pinsir, Thundurus and much more at bay and breaks Sturdy as well as Sashs. Stone Edge is the particularity of this set, and the lure to aforementioned switch-ins. Finally, U-Turn is a pivotal attack that nets supereffective damage on the likes of Latios, Weavile and Alakazam. The speed EVs creep other defensive Landorus-Therians.
Rotom-Wash 
| .washingomatic| Rotom-W |
Levitate | EVs: 240 HP / 252 Def / 16 Spe
Bold Nature | IV: 0 Atk | Pivot, All-Utility
Hydro Pump | Volt Switch | Will-O-Wisp | Pain Split
Rotom-Wash's Will-O-Wisp support complements Intimidate quite well, and the passive damage it deals as well as attack weakening are too good to pass out. Hydro Pump is the go-to attack to take out weakened Pokemon but also on predicted switch-ins. Pain Split allows to play dirty and keep Rotom-Wash healthy against stall teams. Finally, Volt Switch is a pivotal attack that keeps momentum and deals decent damage to Flying-types mainly.
Amoonguss 
| .shroomshields | Amoonguss |
Regenerator | EVs: 248 HP / 168 Def / 92 SpD
Bold Nature | IV: 0 Atk | Pivot, Status, Anti-Setup
Spore | Stun Spore | Giga Drain | Clear Smog
Dual status Amoonguss is rarely expected. Spore puts to sleep a target, so the opponent switches out to another check to Amoonguss, then Stun Spore surprises them and leaves their team with 2 Pokemon crippled. Giga Drain is used to keep the mushroom healthy along with Regenerator's HP boost; finally, Clear Smog deals with setup Pokemon that can't muscle past Amoonguss easily such as CM Keldeo.
Latios 
| .gearshift | Latios |
Levitate | EVs: 4 SpD / 252 Def / 252 SpD
Timid Nature | IV: 0 | Defogger, Revenge Killer
Draco Meteor | Psyshock | Defog | Shadow Ball
Choice Scarf Latios always outruns its enemies and kills them with its powerful attacks but its main function is to use Defog so I can switch freely. Psyshock hits Keldeo, Venusaur, enemy Amoonguss and Lopunny-mega among others for Supereffective damage, while Draco Meteor takes cares of enemy Dragon-types. Finally, Shadow Ball beats Slowbro, Victini and much more Psychic-types which would otherwise switch-in freely.
The End
