Blissey is Brilliant, but ok if you wish, well theres Cresselia,and as Sims suggested Dusknoir, Milotic can be a mixed wall and can help Tangrowth with the fire weakness, Snorlax, Suicune, there are loads.
May i suggest either take out Ludicolo and replace with Starmie, as you lack a Special Sweeper and to block fire attacks better.It is also good in your case due to scary dragons whom often have fire moves in their arsenal.It also can be a Rapid Spinner.
Kingdra could also be ok, but HP Electic and Rain Dance >> Hp Fire and Agility. Rain Dance boost up speed aswell as upping Surf base power, and Hp Electric is just for coverage.
So Something like
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Modest Nature
252 SPEED 252 SP.ATT 6 HP
- Dragon Pulse/Draco meteor
- Hp Electric
- Ice Beam
- Surf
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