Nice team, but as you already know, your team is weak against Fire type.
I suggest you using 
. (Rotom Wash Form)
Rotom wash is the Rotom's form that I personally favor the most. It has only weakness (Grass), and that's thanks to its ability Levitate.
This guy has lots of options of moves:
Stalling:
Item: Sitrus Berry or Lum Berry
Moves:
- Hydro Pump (No need to explain)
- Thunderbolt or Volt Switch
- Pain Split
- Will - O - Wisp
For acting more independently:
Item: Chesto Berry
Moves:
- Hydro Pump (...)
- Thunderbolt or Volt Switch
- Signal Beam / Hidden Power ICE/FIRE
- Rest
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You also can choose to have 
. (Gyarados)
This guy weakens 
(Talonflame) or 
with its ability Intimidate.
Item: Wacan Berry or Sitrus Berry
Moves:
- Waterfall or Aqua Tail(No, do not use Hydro Pump. It does pathetic damage.)
- Earthquake (Type coverage against Electric and Rock types.)
- Dragon Dance or Crunch (If you want Gyarados to act more independently, use Dragon Dance. For move-variety, use Crunch.)
- Ice Fang (Since Gyarados doesn't even learn ideal Flying type moves, It needs a move to defeat Grass types. Ice Fang is also an efficient move to check out for Dragon types.)
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I am also a novice, and the information that I have provided may sound not viable. However, I tried to give you as much information as possible, and I would appreciate any feedbacks.
