Core: Skarmory / Gastrodon / Heatran

Weather basically defines the current BW OU metagame. Whether you like it or not, you'll need some way to deal with all the standard weather archetypes. But that doesn't mean you need to abuse weather yourself. Clear Skies has been shown to be a powerful team style, as long as you include appropriate checks and counters.

Skarmory / Gastrodon / Heatran is an excellent anti-weather core. Team Tabloo is the best example of what this combination is capable of. The three are capable of performing well against Sand, Rain and Sun teams, respectively. However, each individual member of the core is useful at combating at least two of the three weather types, meaning no member's role is too situational.

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Skarmory @ Leftovers

Trait: Sturdy

EVs: 252 HP / 216 Def / 40 Spd

Impish Nature (+Def, -SAtk)

- Brave Bird / Taunt

- Spikes

- Roost

- Whirlwind

Gastrodon @ Leftovers

Trait: Storm Drain

EVs: 252 HP / 4 SAtk / 252 SDef

Calm Nature (+SDef, -Atk)

- Earth Power

- Ice Beam / Scald

- Toxic

- Recover

Heatran @ Leftovers

Trait: Flash Fire

EVs: 252 HP / 248 SDef / 8 Spd

Calm Nature (+SDef, -Atk)

- Stealth Rock

- Lava Plume

- Toxic

- Roar

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Skarmory has always been one of the best physical walls in the game. With access to Spikes and Whirlwind, Skarmory is invaluable as an entry hazard provider. The current metagame is favorable for Skarmory, who can find frequent opportunities to set up or start phazing. Notable threats like Scrafty, Conkeldurr and Excadrill can all be handled by the steel phoenix. Brave Bird breaks Air Balloons and gives Skarmory a 120 BP STAB to work with, but Taunt can be used to shut down other entry hazard users, such as Ferrothorn. 

Despite its RU status, Gastrodon is one of the most valuable Pokémon around. Thanks to Storm Drain and its high Special Defense, it single-handedly walls many Rain sweepers. Burns from the likes of Rotom-W are simply shrugged off with Recover and Leftovers. +2 Thundurus deals only 63.38% - 74.65% with Focus Blast, meaning Gastrodon can function as a solid check to it. Earth Power is Gastrodon's most powerful move, hitting most opponents for good damage. Ice Beam gives Gastrodon a way to eliminate Dragons, but Scald can 
  be helpful for the STAB and potential burns it provides.

Heatran rounds out the core with Stealth Rock and some much-needed Fire coverage. In a metagame full of Steel-type entry hazard users, Heatran can be a very valuable addition to any team. With Lava Plume, Heatran makes life difficult for physical switch-ins like Tyranitar. A 30% burn rate is relatively high in Pokémon, meaning most physical attackers can be crippled by switching in. Toxic gives Heatran something to use against Volcarona, provided it manages to survive being phazed through Stealth Rock damage. Heatran's access to Roar gives the core an excellent second phazer that can take advantage of the switches it forces.

Although this core is solid on its own, it has issues with a few common threats. Late-game Excadrill can be particularly dangerous. If Skarmory is eliminated, weakened, or flinched enough by Rock Slide, the other two members will be swept after a Swords Dance. For this reason, an additional physical wall or powerful priority user is recommended.

Since this core is highly dependent on entry hazards, a spin blocker is also necessary. Gengar performs well in an offensive role, while Jellicent is pretty much the only choice for more defensive players. While both are capable Ghosts, Gengar has the advantage of flawless coverage backed by high Speed and Special Attack stats. When paired with hazard support, Gengar has the potential to sweep teams. Having a Ghost-type also provides a valuable Fighting immunity, which is invaluable against more powerful attackers like Choice Band Terrakion.

Overall, the Skarmory / Gastrodon / Heatran core is a solid combination to use against any type of team. It doesn't require much extra support and can cover a lot of threats on its own. Although weather controls the BW OU metagame, it doesn't have to control your team choices.