A while back I thought it would be fun to see how good of a team I could make making sure to use at least one Pokemon from every generation. I sat down, wrote down my five favorite Pokemon from those generations, then mixed and matched them until I got a team I wanted. I bred the team on Black 2 and took them through the Battle Subway a few times, then went online through the emulator and won seven out of ten battles on OU. So tell me what you think.
Gyarados @ Lum Berry
Trait: Moxie
EVs: 252Atk/4Def/252Spe
Nature: Jolly
~ Ice Fang
~ Waterfall
~ Earthquake
~ Dragon Dance
I never really thought much of Gyarados until Gen 4 redid the physical/special attack mechanics and I started seeing a lot more of them on the emulator. With Dragon Dance Gyarados can become a truly monstrous physical sweeper, better than the rest of them IMO, and with his wide range of moves he has an excellent coverage as well. He has Waterfall for the STAB and Earthquake for the offensive coverage. I originally had him running with Bounce, but I didn't like the accuracy percentage and the fact it take two turns to set up. After a few rather nasty run-ins with Dragonite and Salamence I decided to replace Bounce with Ice Fang due to the type effectiveness on Dragons and the chance for Freezing. My Gyarados has a Jolly Nature so I can make sure he can set up faster than other Dragon Dancers.
Umbreon @ Leftovers
Trait: Synchronize
EVs: 252HP/128Def/128SpD
Nature: Bold
~ Wish
~ Toxic
~ Protect
~ Heal Bell
Umbreon was on my playthrough of Pokemon Gold way back when and even found her way onto my Platinum and Heartgold playthrough teams, simply because I liked how well she could pull off Toxic/Protect. When Gen 5 rolled around and I found out Umbreon could learn Wish AND Heal Bell she made my list and beat the rest of the competition, which included Scizor and Smeargle.
Umbreon is my team healer and pocket-troll in case something happens to Gliscor. She's also great for switching into Pokemon like Blissey who love spamming Toxic and such.
Breloom @ Toxic Orb
Trait: Poison Heal
EVs: 252Atk/4Def/252Spe
Nature: Jolly
~ Spore
~ Substitute
~ Seed Bomb
~ Focus Punch
Like Gyarados, Breloom has a Jolly Nature to give him an edge over other Breloom. At least the ones who aren't running Technician sets with Mach Punch. The Speed EVs and Jolly Nature, I've noticed, also help him outspeed a few of his counters, making it much easier to Spore them. Hit Spore, go into Substitute while they're napping/switching, then Focus Punch or Seed Bomb everything. Even works on Gengar if I can get Substitute set up.
Sableye @ Leftovers
Trait: Prankster
EVs: 252HP/120Def/136SpD
Nature: Calm
~ Taunt
~ Recover
~ Will-O-Wisp
~ Night Shade
Sableye is my UU troll. He's getting promoted to my OU troll. Sableye is my counter for Tricksters and Baton Passers and Dancers and pretty much everything else I don't like. Taunt the Pokemon to stop whatever, use Will-o-Wisp on it or whatever else gets swapped in, and Recover for when the player starts roidraging. The Ghost/Dark combination means nothing is super effective on it. Night Shade, in this case, is better than Foul Play due to the Burn effect of Will-o-Wisp. At one point I had him doing Toxic/Foul Play but his survival rate went way down until I switched back.
Gliscor @ Toxic Orb
Trait: Poison Heal
EVs: 128Atk/252Def/128Spe
Nature: Impish
~ Toxic
~ Protect
~ Substitute
~ Earthquake
Gliscor was a touch choice. I like Gastrodon better because of Stockpile and Recover but unlike Gliscor, Gastrodon can be hit with status afflictions. Gliscor has Poison Heal and Toxic Orb to keep that from happening. He serves the same job as Umbreon, only in an offensive matter with Earthquake. Substitute/Protect keeps almost everything from touching him and with Toxic and Earthquake he can hit pretty much everything.
Volcarona @ Lum Berry
Trait: Swarm
EVs: 252SpA/4SpD/252Spe
Nature: Timid
~ Bug Buzz
~ Quiver Dance
~ Hidden Power [Ground]
~ Flamethrower
Volcarona is my special sweeper. She has Swarm over Flame Body to boost Bug Buzz if I take a nasty hit while Quiver Dancing. I have Flamethrower over Fire Blast because I've had all too many instances where I needed Fire Blast to hit and it refused to. Flamethrower, though less powerful, will hit everything that isn't under Sand Veil or evading. Hidden Power is to take down Fire types that resist Bug Buzz and Flamethrower, like Heatran and Chandelure.

Gyarados @ Lum Berry
Trait: Moxie
EVs: 252Atk/4Def/252Spe
Nature: Jolly
~ Ice Fang
~ Waterfall
~ Earthquake
~ Dragon Dance
I never really thought much of Gyarados until Gen 4 redid the physical/special attack mechanics and I started seeing a lot more of them on the emulator. With Dragon Dance Gyarados can become a truly monstrous physical sweeper, better than the rest of them IMO, and with his wide range of moves he has an excellent coverage as well. He has Waterfall for the STAB and Earthquake for the offensive coverage. I originally had him running with Bounce, but I didn't like the accuracy percentage and the fact it take two turns to set up. After a few rather nasty run-ins with Dragonite and Salamence I decided to replace Bounce with Ice Fang due to the type effectiveness on Dragons and the chance for Freezing. My Gyarados has a Jolly Nature so I can make sure he can set up faster than other Dragon Dancers.

Umbreon @ Leftovers
Trait: Synchronize
EVs: 252HP/128Def/128SpD
Nature: Bold
~ Wish
~ Toxic
~ Protect
~ Heal Bell
Umbreon was on my playthrough of Pokemon Gold way back when and even found her way onto my Platinum and Heartgold playthrough teams, simply because I liked how well she could pull off Toxic/Protect. When Gen 5 rolled around and I found out Umbreon could learn Wish AND Heal Bell she made my list and beat the rest of the competition, which included Scizor and Smeargle.
Umbreon is my team healer and pocket-troll in case something happens to Gliscor. She's also great for switching into Pokemon like Blissey who love spamming Toxic and such.

Breloom @ Toxic Orb
Trait: Poison Heal
EVs: 252Atk/4Def/252Spe
Nature: Jolly
~ Spore
~ Substitute
~ Seed Bomb
~ Focus Punch
Like Gyarados, Breloom has a Jolly Nature to give him an edge over other Breloom. At least the ones who aren't running Technician sets with Mach Punch. The Speed EVs and Jolly Nature, I've noticed, also help him outspeed a few of his counters, making it much easier to Spore them. Hit Spore, go into Substitute while they're napping/switching, then Focus Punch or Seed Bomb everything. Even works on Gengar if I can get Substitute set up.

Sableye @ Leftovers
Trait: Prankster
EVs: 252HP/120Def/136SpD
Nature: Calm
~ Taunt
~ Recover
~ Will-O-Wisp
~ Night Shade
Sableye is my UU troll. He's getting promoted to my OU troll. Sableye is my counter for Tricksters and Baton Passers and Dancers and pretty much everything else I don't like. Taunt the Pokemon to stop whatever, use Will-o-Wisp on it or whatever else gets swapped in, and Recover for when the player starts roidraging. The Ghost/Dark combination means nothing is super effective on it. Night Shade, in this case, is better than Foul Play due to the Burn effect of Will-o-Wisp. At one point I had him doing Toxic/Foul Play but his survival rate went way down until I switched back.

Gliscor @ Toxic Orb
Trait: Poison Heal
EVs: 128Atk/252Def/128Spe
Nature: Impish
~ Toxic
~ Protect
~ Substitute
~ Earthquake
Gliscor was a touch choice. I like Gastrodon better because of Stockpile and Recover but unlike Gliscor, Gastrodon can be hit with status afflictions. Gliscor has Poison Heal and Toxic Orb to keep that from happening. He serves the same job as Umbreon, only in an offensive matter with Earthquake. Substitute/Protect keeps almost everything from touching him and with Toxic and Earthquake he can hit pretty much everything.

Volcarona @ Lum Berry
Trait: Swarm
EVs: 252SpA/4SpD/252Spe
Nature: Timid
~ Bug Buzz
~ Quiver Dance
~ Hidden Power [Ground]
~ Flamethrower
Volcarona is my special sweeper. She has Swarm over Flame Body to boost Bug Buzz if I take a nasty hit while Quiver Dancing. I have Flamethrower over Fire Blast because I've had all too many instances where I needed Fire Blast to hit and it refused to. Flamethrower, though less powerful, will hit everything that isn't under Sand Veil or evading. Hidden Power is to take down Fire types that resist Bug Buzz and Flamethrower, like Heatran and Chandelure.