There aren't really any good fire/grass decks, but for just water/fire, Ludicargo works.
3 Plusle DX
1 Jirachi DX
3 Lotad DX35
1 Lombre DX33
1 Lombre DX34
3 Ludicolo DX10
2 Slugma DX74
2 Magcargo DX20
2 Vulpix HL
2 Ninetails HL
4 Celio's Network
3 Steven's Advice
2 Copycat
2 Rocket's Admin.
4 Battle Frontier
3 Rare Candy
1 Mr. Briney's Compassion
1 Ancient Technical Machine Rock
3 Swoop! Teleporter
4 Water Energy
2 Fire Energy
3 Rainbow Energy
4 Double Rainbow Energy
2 Heal Energy
2 Scramble Energy
Feel free to change the ninetales to Rhydon HL, Grumpig DX, Marowak FRLG, Lanturn HL, Banette ex, or any other well-damaging stage 1, really. Change the fires to the energy the stage 1 needs, and if it's an ex, take off 1 double rainbow energy for a regular Rainbow energy.