I've been trying to create a team based around Dragonite, and the following team seems to be doing well in Pokemon Showdown, but there is always room for improvement. I'm hovering around the 1670 level but that number involved using other teams before so that number is not as accurate.
This team is the first one where I've had several Pokemon try to support one or two others on the team, as opposed to a balanced team or a straight offense team, and I think this type of team works well.
The team:
Ferrothorn @ Focus Sash
Brave, Iron Barbs
252Atk / 252Def / 4SDef
Spikes
Leech Seed
Power Whip
Thunder Wave
I typically lead with Ferrothorn, but sometimes I'll use someone else, depending on the Team Preview. Ferrothorn is seen so often on OU teams that I have decided to try something slightly different. Instead of giving it Leftovers or Rocky Helmet, I gave it a Focus Sash... which means that I can put all the HP EVs into Attack instead. Sometimes I don't expect a Pokemon to have a Fire type move and I lose Ferrothorn before it can set up its Spikes, so at least this way, I can let it survive through at least one turn. Thunder Wave is typically helpful when paralysis activates and if Ferrothorn survives, it can spread the fun. I gave Ferrothorn Leech Seed so that if it comes across an opposing Dragonite before Stealth Rock is set, I can nullify its Multiscale despite a potential Roost and/or Leftovers, and let my other Pokemon deal with it (most likely Mamoswine).
Synergy:
Fire -> Starmie, Dragonite
Fighting -> Starmie, Dragonite, Espeon, Volcarona
Mamoswine @ Focus Sash
Adamant, Snow Cloak
4HP / 252 Atk / 252 Speed
Earthquake
Ice Shard
Stealth Rock
Endeavor/Roar
Mamoswine is my answer to opposing Dragon types that outspeed my Dragonite. It has Stealth Rock since I use it as my auxiliary lead if I feel that Ferrothorn should hold back, and it has the typical Earthquake and Ice Shard combination. I gave it a Focus Sash as well. For the last move, I'm not sure if Endeavour or Roar would be the better option, if at all. I've rarely used the move in competitive battles. Focus Sash, Endeavor and Ice Shard would work great if an opposing Skarmory or Bronzong somehow got Mamoswine to 1 HP, I suppose.
Synergy:
Steel -> Ferrothorn, Volcarona
Fighting -> Starmie, Dragonite, Espeon, Volcarona
Fire -> Starmie, Dragonite
Water -> Starmie, Dragonite, Ferrothorn
Dragonite @ Life Orb
Mild, Multiscale
252 Atk / 252 SpA / 4 Speed
Draco Meteor
Fire Blast
Superpower
Extremespeed
Dragonite is the team's mascot, thus, this is a given. At first, I wanted to use the Dragon Dance physical attacker version but I found that I was stopped by the likes of Gliscor and other physical walls, so this led me to use the classic mixed attacker Dragonite, and thanks to BW2, Dragonite can have Superpower with Multiscale. Draco Meteor is to inflict a lot of damage to non-steel types, Fire Blast is for the steel types, Superpower is for Blissey, Chansey, and Heatran, and Extremespeed is for +2 priority over Choice Scarfed Pokemon who have a higher base speed or Pokemon who only have +1 priority. I'm using Life Orb to get in more damage but I'm wondering about the synergy with Multiscale, but Inner Focus doesn't seem to be a much better option since Dragonite's not going to be a lead that potentially faces Fake Out. I'm also concerned about how Draco Meteor and Superpower lower offensive stats, which usually get me to switch out Dragonite more frequently than I would like, and Stealth Rock will be a bane. Thus, I will need a spinner and a dual screener.
Synergy:
Dragon -> Ferrothorn
Ice -> Starmie, Volcarona
Rock -> Ferrothorn
Starmie @ Life Orb
Timid, Natural Cure
4 HP / 252 SpA / 252 Speed
Surf
Thunderbolt
Ice Beam
Rapid Spin
Starmie has access to Rapid Spin. Three Pokemon on the team desperately want a clear field so that move is essential. Starmie resists Ice attacks which Dragonite does not like, so I thought it was a great choice. Surf for an accurate STAB attack, Thunderbolt and Ice Beam for coverage.
Synergy:
Bug -> Volcarona, Dragonite
Electric -> Mamoswine, Ferrothorn
Grass -> Volcarona, Ferrothorn, Dragonite
Dark -> Ferrothorn
Ghost -> Ferrothorn
Espeon @ Light Clay
Calm, Magic Bounce
4 HP / 252 SpA / 252 Speed
Psychic
Hidden Power Fighting
Light Screen
Reflect
I chose Espeon to support Dragonite with dual screens, as well as use its Magic Bounce to stop new hazards or moves which serve only to induce permanent status. Psychic is the STAB attack, and Hidden Power Fighting serves to attack Steel and Dark types that Psychic cannot dent. In the past few battles, though, I've kept Espeon away from battle because I keep seeing opportunities for another sweeper to come in without the need of screens.
Synergy:
Bug -> Volcarona, Dragonite
Dark -> Ferrothorn
Ghost -> Ferrothorn
Volcarona @ Leftovers
Timid, Flame Body
252 SpA / 4 SpD / 252 Speed
Bug Buzz
Fiery Dance
Quiver Dance
Hidden Power Ground
For instance, if the field is clear of hazards, I may decide to switch in Volcarona and begin a Quiver Dance while the opponent switches. Volcarona is a great Pokemon if my opponent does not have any physical sweepers with priority left. I've given it Hidden Power Ground instead of Rock because most of my opponents send in Heatran or Terrakion to respond to Volcarona. This Pokemon is my backup plan in case Dragonite falls early.
Synergy:
Water-> Starmie, Dragonite, Ferrothorn
Rock -> Ferrothorn
Flying -> NONE
Team's weaknesses that I've found:
When playing this team, I've noticed that Tornadus can spam Hurricane while in a rain team and pretty much destroy the team bar Mamoswine, but Mamoswine is usually taken out pretty quickly in the rain, especially when a lucky Scald burns it while it's on its Sash.
Jirachi also loves to paraflinch a lot, and Dragonite is slower than the Jirachi as it is. Starmie needs 2 to 3 Surfs to defeat Jirachi, while Jirachi's well-placed Thunder or the rare Psychic fells Starmie in 1 hit.
I have trouble against Swords Dance Scizor, despite having Volcarona on the team, but maybe that's just my play style and always thinking Scizor's a Choice Band variant.
Hail and Sandstorm teams make wear on my Dragonite that doesn't have any recovery and the former weather nullifies the need for Ferrothorn's sash, who probably didn't need it to go against a hail team and thus wasted a hold item spot.
Having no spin blocker, despite having two hazard layers and a reliance on residual damage if Dragonite has reduced stats, seems like a foolish move, but I'm not sure who I should replace, if anyone.
Status ailments really wreck my team's longevity, since Dragonite and Starmie use Life Orb (Starmie can use Natural Cure but that's giving a free turn), and even with Espeon stopping Toxic, Thunder Wave, Will-o-Wisp, Spore, and Confuse Ray, it can't stop secondary effects of attacks.
Ferrothorn is listed as a synergistic partner for a lot of the RMT, but again, I don't find that Ferro lasts too long... again, it might be my play style.
Please give your comments.
This team is the first one where I've had several Pokemon try to support one or two others on the team, as opposed to a balanced team or a straight offense team, and I think this type of team works well.
The team:

Ferrothorn @ Focus Sash
Brave, Iron Barbs
252Atk / 252Def / 4SDef
Spikes
Leech Seed
Power Whip
Thunder Wave
I typically lead with Ferrothorn, but sometimes I'll use someone else, depending on the Team Preview. Ferrothorn is seen so often on OU teams that I have decided to try something slightly different. Instead of giving it Leftovers or Rocky Helmet, I gave it a Focus Sash... which means that I can put all the HP EVs into Attack instead. Sometimes I don't expect a Pokemon to have a Fire type move and I lose Ferrothorn before it can set up its Spikes, so at least this way, I can let it survive through at least one turn. Thunder Wave is typically helpful when paralysis activates and if Ferrothorn survives, it can spread the fun. I gave Ferrothorn Leech Seed so that if it comes across an opposing Dragonite before Stealth Rock is set, I can nullify its Multiscale despite a potential Roost and/or Leftovers, and let my other Pokemon deal with it (most likely Mamoswine).
Synergy:
Fire -> Starmie, Dragonite
Fighting -> Starmie, Dragonite, Espeon, Volcarona

Mamoswine @ Focus Sash
Adamant, Snow Cloak
4HP / 252 Atk / 252 Speed
Earthquake
Ice Shard
Stealth Rock
Endeavor/Roar
Mamoswine is my answer to opposing Dragon types that outspeed my Dragonite. It has Stealth Rock since I use it as my auxiliary lead if I feel that Ferrothorn should hold back, and it has the typical Earthquake and Ice Shard combination. I gave it a Focus Sash as well. For the last move, I'm not sure if Endeavour or Roar would be the better option, if at all. I've rarely used the move in competitive battles. Focus Sash, Endeavor and Ice Shard would work great if an opposing Skarmory or Bronzong somehow got Mamoswine to 1 HP, I suppose.
Synergy:
Steel -> Ferrothorn, Volcarona
Fighting -> Starmie, Dragonite, Espeon, Volcarona
Fire -> Starmie, Dragonite
Water -> Starmie, Dragonite, Ferrothorn

Dragonite @ Life Orb
Mild, Multiscale
252 Atk / 252 SpA / 4 Speed
Draco Meteor
Fire Blast
Superpower
Extremespeed
Dragonite is the team's mascot, thus, this is a given. At first, I wanted to use the Dragon Dance physical attacker version but I found that I was stopped by the likes of Gliscor and other physical walls, so this led me to use the classic mixed attacker Dragonite, and thanks to BW2, Dragonite can have Superpower with Multiscale. Draco Meteor is to inflict a lot of damage to non-steel types, Fire Blast is for the steel types, Superpower is for Blissey, Chansey, and Heatran, and Extremespeed is for +2 priority over Choice Scarfed Pokemon who have a higher base speed or Pokemon who only have +1 priority. I'm using Life Orb to get in more damage but I'm wondering about the synergy with Multiscale, but Inner Focus doesn't seem to be a much better option since Dragonite's not going to be a lead that potentially faces Fake Out. I'm also concerned about how Draco Meteor and Superpower lower offensive stats, which usually get me to switch out Dragonite more frequently than I would like, and Stealth Rock will be a bane. Thus, I will need a spinner and a dual screener.
Synergy:
Dragon -> Ferrothorn
Ice -> Starmie, Volcarona
Rock -> Ferrothorn

Starmie @ Life Orb
Timid, Natural Cure
4 HP / 252 SpA / 252 Speed
Surf
Thunderbolt
Ice Beam
Rapid Spin
Starmie has access to Rapid Spin. Three Pokemon on the team desperately want a clear field so that move is essential. Starmie resists Ice attacks which Dragonite does not like, so I thought it was a great choice. Surf for an accurate STAB attack, Thunderbolt and Ice Beam for coverage.
Synergy:
Bug -> Volcarona, Dragonite
Electric -> Mamoswine, Ferrothorn
Grass -> Volcarona, Ferrothorn, Dragonite
Dark -> Ferrothorn
Ghost -> Ferrothorn

Espeon @ Light Clay
Calm, Magic Bounce
4 HP / 252 SpA / 252 Speed
Psychic
Hidden Power Fighting
Light Screen
Reflect
I chose Espeon to support Dragonite with dual screens, as well as use its Magic Bounce to stop new hazards or moves which serve only to induce permanent status. Psychic is the STAB attack, and Hidden Power Fighting serves to attack Steel and Dark types that Psychic cannot dent. In the past few battles, though, I've kept Espeon away from battle because I keep seeing opportunities for another sweeper to come in without the need of screens.
Synergy:
Bug -> Volcarona, Dragonite
Dark -> Ferrothorn
Ghost -> Ferrothorn

Volcarona @ Leftovers
Timid, Flame Body
252 SpA / 4 SpD / 252 Speed
Bug Buzz
Fiery Dance
Quiver Dance
Hidden Power Ground
For instance, if the field is clear of hazards, I may decide to switch in Volcarona and begin a Quiver Dance while the opponent switches. Volcarona is a great Pokemon if my opponent does not have any physical sweepers with priority left. I've given it Hidden Power Ground instead of Rock because most of my opponents send in Heatran or Terrakion to respond to Volcarona. This Pokemon is my backup plan in case Dragonite falls early.
Synergy:
Water-> Starmie, Dragonite, Ferrothorn
Rock -> Ferrothorn
Flying -> NONE
Team's weaknesses that I've found:
When playing this team, I've noticed that Tornadus can spam Hurricane while in a rain team and pretty much destroy the team bar Mamoswine, but Mamoswine is usually taken out pretty quickly in the rain, especially when a lucky Scald burns it while it's on its Sash.
Jirachi also loves to paraflinch a lot, and Dragonite is slower than the Jirachi as it is. Starmie needs 2 to 3 Surfs to defeat Jirachi, while Jirachi's well-placed Thunder or the rare Psychic fells Starmie in 1 hit.
I have trouble against Swords Dance Scizor, despite having Volcarona on the team, but maybe that's just my play style and always thinking Scizor's a Choice Band variant.
Hail and Sandstorm teams make wear on my Dragonite that doesn't have any recovery and the former weather nullifies the need for Ferrothorn's sash, who probably didn't need it to go against a hail team and thus wasted a hold item spot.
Having no spin blocker, despite having two hazard layers and a reliance on residual damage if Dragonite has reduced stats, seems like a foolish move, but I'm not sure who I should replace, if anyone.
Status ailments really wreck my team's longevity, since Dragonite and Starmie use Life Orb (Starmie can use Natural Cure but that's giving a free turn), and even with Espeon stopping Toxic, Thunder Wave, Will-o-Wisp, Spore, and Confuse Ray, it can't stop secondary effects of attacks.
Ferrothorn is listed as a synergistic partner for a lot of the RMT, but again, I don't find that Ferro lasts too long... again, it might be my play style.
Please give your comments.