After having a really awful Win/Loss in the last season of Battle Spot, seeing that losing streak starting to happen again, and my general desire to get revenge on lazy yet powerful sets, I read several strategies online, did some tinkering, and devised a team for myself to handle most threats on Singles. The Pokemon viewer on the Global Link was very helpful in showing me what the most common Pokemon used were and was integral in helping me design this team. I went from a 5/8 to a 25/20 with this team:
Haxorus @ Lum Berry
4 HP/252 Atk/252 Spe
Ultimately, kinda useless outside of some Fairy threats like Azumarill and Whimsicott. I rarely bring it into battle and might end up replacing it someday, but it's still VERY powerful once it gets a DD up. Most common uses involve making an opponent safely switch to their Fairy type...only to get a DD boosted EQ or PJ to the face. Lum prevents Whimsicott-related status-ery.
Gyarados @ Life Orb
252 Atk/4 Def/252 Spe
This is usually why Haxorus doesn't see much play. Once Gyarados gets off a DD there isn't a single thing that isn't a wall that can take anything boosted by Life Orb. The problems that Gyarados commonly faces are Mega Venusaur, Rotom (before DD), and Porygon 2, but usually these can be avoided by a switch to a Pokemon that can take their hits. Speaking of switching, there is a reason other than "I forgot to get a Hidden Ability Magikarp" as to why I run Intimidate over Moxie. Moxie would be very helpful in sweeping, but...
Manectric @ Manectite
Lightningrod (Reg)/ Intimidate (Mega)
4 Def/252 SpA/252 Spe
Hidden Power (Ice)
Ever since I was first introduced to Doubles, I always wanted to run a Gyarados-Manectric combo. Having Lightningrod to absorb all of the electric attacks heading to Gyarados was an extremely appealing idea to me. However, Manectric got to be pretty bad once 4th and 5th rolled around due to everything having a base speed of 106+ and having access to Ground STAB, so I really only got to use the combination in XD. In Story Mode.
135/135 special sweeper with Intimidate is way too good to pass up. Even though it's not Doubles the combination still works fantastically. Electric type with Levitate switches in on Gyarados? Switch to regular Manectric and get +1 in Special Attack for the low cost of no damage. Want to annoy users of the best starting bird since 4th gen? Get a chain of Intimidates going with Volt Switch just in case it somehow lives a 70 BP electric STAB move. Also, even with no boosts, I have often seen HP Ice OHKO a Garchomp. Just be mindful of Weakness Policy Dragonite and Aegislash. You might think you can KO them, but they can tank some powerful hits and get some crazy damage going. Just use your head on what to do when something like that happens. Also, go for 4 Defense EVs because the spread for HP Ice requires a 30 in Defense (31/x/30/31/31/31). I have seen Mega Manectric live some physical attacks it otherwise wouldn't because of that. These two usually see the most use in battle.
Heatran @ Choice Specs
4 HP/252 SpA/252 Spe
Hidden Power (Grass OR Electric)
Admittedly, this is probably a really hard Pokemon to obtain like this if you don't know how to RNG, use Pokegen, or use a DNS spoofing site, so it's probably the biggest hurdle in regards to making this team. Specs Heatran can do some monstrous damage even if the hit is resisted. The HP type is dependent on if you hate Swampert/Quagsire or Talonflame/Non-Mega Gyarados more. If you run HP Grass like I do, you can probably still 1-2HKO a Talonflame with Fire Blast. Make sure Heatran is either used very early game, so you can switch in case of a bad move choice, or when the opponent no longer has a hidden Pokemon on their team and you can plan accordingly. Heatran is the second-least used Pokemon on my team, but when it shows up, it usually ends up being the MVP. Very handy against Mega-Venusaur, Scizor, and Aegislash.
Whimsicott @ Wide Lends or Leftovers
252 HP/252 Def/4 Spe
Whimsicott is probably the main reason why the metagame shifted to using more Mega Venusaur after Pokebank was released. It has a very nasty priority paralysis and the ability to shut down other leads that don't have Magic Bounce. (REMINDER: Taunt is blocked by Magic Bounce. I know this because Science.) Use Whimsicott when the opponent has a lack of Grass and Electric types on their team. I use Wide Lens to help make sure some crucial Stun Spores hit the opponent, because if you base your strategy around that for the entire game and it misses on, say, Gengar, Whimsicott is going down and you lose. You just lose. Leftovers can help with recovery in case of a Porygon 2 stallfest, but ultimately, Wide Lens helps a lot more. Use Stun Spore on sweepers and use Tauntcore on walls and other annoyances. Moonblast is just for coverage in the rare case of Whimsicott being the last Pokemon. It destroys Garchomp with a 97 Special Attack stat and a 95 BP move. Trust me. You could run U-Turn but then you have a cotton ball hitting a brick wall for the remaining twenty minutes.
Gliscor @ Toxic Orb
252 HP/164 Atk/72 Spe
Gliscor isn't used that often, but when it is, it's probably going to do something good. It completely walls physical attackers, electric types that aren't carrying HP Ice, Aegislash, other walls, and the entire country of Denmark. (I'm assuming, anyway. That person didn't know what to do against mine.) Gliscor usually comes in when you can't use Whimsicott or Gyarados due to the opponent's team being filled with things that would likely stop them before they could do any work. It meshes well with every Pokemon on the team except Haxorus, who has very similar weaknesses and strengths. Special Attackers, especially those that use ice type moves, are the bane of its existence, so keep that in mind at the team preview. Gliscor can ruin physical walls almost as well as Whimsicott with Knock Off, but remember to look out for Weakness Policy Aegislash. (Although, Gliscor did live a +4 Shadow Sneak from the thing with 35 HP so who knows if it's actually a threat or not.) You can run Toxic over Ice Fang to get some more damage on other walls, but the Ice Fang is usually unexpected and I've actually had people try to set up dragon types on me predicting a switch or a Substitute. It did not go well for them.
Feel free to use it if you want. I've been having a lot of fun on Battle Spot with it, and I haven't even had a DC yet. It's powerful but not broken, so most people just feel like they made some mistakes and didn't lose to hax. Much better than my 1 Win/1 Loss/1 DC record when I used to use Lockdown the Klefki.