To get a few things straight: You made a Doubles team with 3 sweepers
and 1 wall In Doubles you need bulk and need to be prepared of getting
double targetted since spread moves will be used much more.
First of all: Kingdra
To be honest get rid of it and replace it with Hydreigon
Hydreigon(F) @ Dragon Gem
EVs: 60 HP / 252 SAtk /196 Spd
- Draco Meteor
- Dark Pulse
Draco Meteor + Dragon Gem kills almost everything that doesn't resist it. Dark Pulse for Psychic and Ghost. Flamethrower for the Steels (except Heatran). Protect to dodge attacks or Surf to get boosted in the Rain. I would go for Protect
If you are running this in Rain This teammember is a replacement for Jolteon:
Rotom-Wash @ Chesto Berry
EVs: 252 HP / 252 SAtk / 4 SDef
- Hydro Pump
- Volt Switch/ Hidden Power
Taking down opponents with his STAB Hydro Pumps when the rain is up is almost everytime a KO. Discharge to hit multiple Pokemon. Rest for a instant heal. Volt Switch for scouting or a Hidden Power of choice.
Bronzong @ Damp Rock
EVs: 252 HP / 252 Atk / 4 SAtk
IVs: 0 Spd
- Rain Dance
- Light Screen
A Steel type was needed to resist the Dragon Gem + Draco Meteors flying around your head (Hydreigon and [email protected]). Earthquake to hit multiple opponents. Because most of your team is imunne to Earthquake it isnt a really big deal. Psyshock for punching Blissey and Chansey in her face. Rain Dance for getting the rain up and Light Screen to protect yourself against the special attacks since your team is more vurneable to that.
Mamoswine @ Choice Band
Trait: Thick Fat
EVs: 252 HP / 252 Atk / 4 SDef
- Ice Shard
- Rock Slide
A strategy often used in Doubles is the DisQuake combo. Rotom-W together with Mamo as lead for the DisQuake combo. Ice Shard for priority and STAB. Superpower to kill Heatran on the switch and TTar. Rock Slide to give the EdgeQuake Combo. Choice Band to hit hard. Could be replaced with Life Orb.
Note: Bronzong could be replaced with Metagross and Mamoswine for another Ground type.
I tested this team against my own team and even if Mamoswine is killed with a Dragon Gem Draco Meteor there is still a possibility to win.
Good luck :)