This has been netting me quite a few wins lately, and it's pretty decent but there are some large gaps which I hope you can all help me patch up. 
At a glance...
Update:
--->
In depth...
Roserade (F) @ Choice Scarf
Ability: Natural Cure
EVs: 252 Spd/252 SAtk/6 SDef
Timid nature (+Spd, -Atk)
- Sleep Powder
- Leaf Storm
- Hidden Power [Ice]
- Sludge Bomb
Stops a lot of leads cold. It's current EVs and nature give it a speed stat of 459, giving it priority over basically all leads. By sleeping on turn, I've delayed Stealth Rocks probably and already disabled on of their pokemon. Only trouble it may come into would be the rare Lum Berry lead (Not that I've seen any...). Swampert leads are KO'd with Leaf Storm if they don't run, and Sludge Bomb is there for STAB and coverage over Celebi who is KO / close to it. Makes a decent Dragon revenge killer with it's high speed, which many people don't expect and keep their dragons in anways.
Heatran (M) @ Expert Belt
Ability: Flash Fire
EVs: 6 HP/252 Spd/252 SAtk
Timid nature (+Spd, -Atk)
- Earth Power
- Fire Blast
- Taunt
- Substitute
SubTran is amazing, don't know why I never used this before! With Substitute it's able to get the one-up on faster threats when they switch in. It's my second switch Scizor who, like I said, is great Substitute bait. With Taunt I'm able to stop DDMence and DDGyara, as well I've found Taunting Blissey + Switching to Tyranitar to he a good combo, as they Pursuit will kill Blissey if it stays (3-4KO I believe) in because of lack of Softboiled / Wish, as well as deal a considerable amount of damage to a fleeing one. All in all, a lot more helpful than Hidden Power Ice.
Bronzong @ Leftovers
Ability: Levitate
EVs: 252 HP/86 Atk/80 Def/92 SDef
Sassy nature (+SDef, -Spd)
- Gyro Ball
- Stealth Rock
- Earthquake
- Reflect / Light Screen
Well, I decided to write out the entire threat list and what (on my team) handles each of those. Of course I found a couple which totally shred me up, but they all had something in common - Bronzong counter them, easy! Salamence, Togekiss, and Mamoswine are now much more easily handled. Pretty standard set, except I decided to drop Hypnosis for Reflect as I already have a sleeper in Roserade. Stealth Rock provides some good support, as it'll wear down Dragonite who can be bothersome as well as some [obvious] others. I'm wondering if Light Screen would be more useful, as it will soften up Fire Blasts from Mence?
Latias (F) @ Leftovers
Ability: Levitate
EVs: 150 HP/252 Spd/108 SAtk
Timid nature (+Spd, -Atk)
- Calm Mind
- Recover
- Dragon Pulse
- Substitute
Comes out later on the match once I know my opponents team better, and when Scizor and his pursuit friends (Heracross, Tyranitar, Metagross) are dead and gone. CMLatias is ridiculous, and unless they can get rid of it quickly it's pretty much game set and match. Turns Heatran, Blissey, Zapdos (just to name a few) into set-up fodder as they are utterly useless in trying to take it down, as the only means possible is Toxic but by throwing up a Substitute, I block that out. As well as giving me time to Calm Mind safely and scout for Pursuit. I've found if Swampert doesn't have Ice Punch, I can set-up on him too (Stone Edge is easily stalled out with Recover, factoring in it's shaky accuracy and 8pp). Tears apart teams who were silly enough to let me get some Calm Minds in.
Tyranitar (M) @ Choice Band
Ability: Sand Stream
EVs: 178 HP/252 Atk/80 SDef
Adamant nature (+Atk, -SAtk)
- Aqua Tail
- Stone Edge
- Crunch
- Pursuit
aka ass-kicker. Tyranitar rips shit-up, easily coming in on frail choice users who got stuck in the wrong attack and Pursuiting them to hell (Bye-bye Jolteon). I relocated 80 Spe EVs to SpD, because I don't really care for Tyranitar to be fast, and it gives it some extra bulk against special-attackers. My Latias 'counter', but it can only take down the Calm Mind variants, the Specs sweeper is too much to handle.
Rotom-h @ Leftovers
Ability: Levitate
EVs: 252 HP/168 Def/90 Spd
Bold nature (+Def, -Atk)
- Discharge
- Shadow Ball
- Overheat
- Will-O-Wisp / Light Screen
Steel check and counter, now that Bronzong carries Reflect I can pack WoW for nasty little Swampert, though I am not a huge fan... I can't deny burning the likes of Tyranitar, Lucario, and so on. Pseudo-dual status with Discharge as I realized the base power really isn't that much different from Thunderbolts, and I believe the paralysis makes up for the miss on a few hits (Such as on Togekiss).
So yeah, there it is! I have been winning quite frequently with this team, but I feel there is more potential. I'm hoping I can make this team more defensively sound. I'm not sure of there are any threats I didn't at least partially cover, so any help and comments are appreciated!
EDIT: Sorry if there are really awkward spelling errors and sentences, as I have this problem where I type faster than I think and end up missing words or typing something completely different.

At a glance...






Update:


In depth...

Roserade (F) @ Choice Scarf
Ability: Natural Cure
EVs: 252 Spd/252 SAtk/6 SDef
Timid nature (+Spd, -Atk)
- Sleep Powder
- Leaf Storm
- Hidden Power [Ice]
- Sludge Bomb
Stops a lot of leads cold. It's current EVs and nature give it a speed stat of 459, giving it priority over basically all leads. By sleeping on turn, I've delayed Stealth Rocks probably and already disabled on of their pokemon. Only trouble it may come into would be the rare Lum Berry lead (Not that I've seen any...). Swampert leads are KO'd with Leaf Storm if they don't run, and Sludge Bomb is there for STAB and coverage over Celebi who is KO / close to it. Makes a decent Dragon revenge killer with it's high speed, which many people don't expect and keep their dragons in anways.

Heatran (M) @ Expert Belt
Ability: Flash Fire
EVs: 6 HP/252 Spd/252 SAtk
Timid nature (+Spd, -Atk)
- Earth Power
- Fire Blast
- Taunt
- Substitute
SubTran is amazing, don't know why I never used this before! With Substitute it's able to get the one-up on faster threats when they switch in. It's my second switch Scizor who, like I said, is great Substitute bait. With Taunt I'm able to stop DDMence and DDGyara, as well I've found Taunting Blissey + Switching to Tyranitar to he a good combo, as they Pursuit will kill Blissey if it stays (3-4KO I believe) in because of lack of Softboiled / Wish, as well as deal a considerable amount of damage to a fleeing one. All in all, a lot more helpful than Hidden Power Ice.

Bronzong @ Leftovers
Ability: Levitate
EVs: 252 HP/86 Atk/80 Def/92 SDef
Sassy nature (+SDef, -Spd)
- Gyro Ball
- Stealth Rock
- Earthquake
- Reflect / Light Screen
Well, I decided to write out the entire threat list and what (on my team) handles each of those. Of course I found a couple which totally shred me up, but they all had something in common - Bronzong counter them, easy! Salamence, Togekiss, and Mamoswine are now much more easily handled. Pretty standard set, except I decided to drop Hypnosis for Reflect as I already have a sleeper in Roserade. Stealth Rock provides some good support, as it'll wear down Dragonite who can be bothersome as well as some [obvious] others. I'm wondering if Light Screen would be more useful, as it will soften up Fire Blasts from Mence?

Latias (F) @ Leftovers
Ability: Levitate
EVs: 150 HP/252 Spd/108 SAtk
Timid nature (+Spd, -Atk)
- Calm Mind
- Recover
- Dragon Pulse
- Substitute
Comes out later on the match once I know my opponents team better, and when Scizor and his pursuit friends (Heracross, Tyranitar, Metagross) are dead and gone. CMLatias is ridiculous, and unless they can get rid of it quickly it's pretty much game set and match. Turns Heatran, Blissey, Zapdos (just to name a few) into set-up fodder as they are utterly useless in trying to take it down, as the only means possible is Toxic but by throwing up a Substitute, I block that out. As well as giving me time to Calm Mind safely and scout for Pursuit. I've found if Swampert doesn't have Ice Punch, I can set-up on him too (Stone Edge is easily stalled out with Recover, factoring in it's shaky accuracy and 8pp). Tears apart teams who were silly enough to let me get some Calm Minds in.

Tyranitar (M) @ Choice Band
Ability: Sand Stream
EVs: 178 HP/252 Atk/80 SDef
Adamant nature (+Atk, -SAtk)
- Aqua Tail
- Stone Edge
- Crunch
- Pursuit
aka ass-kicker. Tyranitar rips shit-up, easily coming in on frail choice users who got stuck in the wrong attack and Pursuiting them to hell (Bye-bye Jolteon). I relocated 80 Spe EVs to SpD, because I don't really care for Tyranitar to be fast, and it gives it some extra bulk against special-attackers. My Latias 'counter', but it can only take down the Calm Mind variants, the Specs sweeper is too much to handle.

Rotom-h @ Leftovers
Ability: Levitate
EVs: 252 HP/168 Def/90 Spd
Bold nature (+Def, -Atk)
- Discharge
- Shadow Ball
- Overheat
- Will-O-Wisp / Light Screen
Steel check and counter, now that Bronzong carries Reflect I can pack WoW for nasty little Swampert, though I am not a huge fan... I can't deny burning the likes of Tyranitar, Lucario, and so on. Pseudo-dual status with Discharge as I realized the base power really isn't that much different from Thunderbolts, and I believe the paralysis makes up for the miss on a few hits (Such as on Togekiss).
So yeah, there it is! I have been winning quite frequently with this team, but I feel there is more potential. I'm hoping I can make this team more defensively sound. I'm not sure of there are any threats I didn't at least partially cover, so any help and comments are appreciated!
EDIT: Sorry if there are really awkward spelling errors and sentences, as I have this problem where I type faster than I think and end up missing words or typing something completely different.