Mosmer

Well I used totally different Pokemons but they mighy help you.. Male Meowstic w/Prankster, the fusion of Solrock and Lunatone, a Pokemon w/Surf and 3 Pokemons you like, you can get all of them prior to the fight. Use Light Screen w/ Meowstic and Surf w/ the surfing Pokemon so you lower their accuracy, once Meowstic faints send Solrock and sweep w/ Cosmic Power x6 (healing when needed and using revive on Meowstic if you can) after that its all easy, eventually the sun will fade and you can bulldoze everything she has.. PD: One of the Sludge TM is in the corrupted cave can't remember which exactly..

Well it seems like almost everybody understimates Meowstic... A prankster Meowstic (male) @Light Clay w/ Light Screen and Misty Terrain (lvl 50 then reverse candy) can take away the water at least for a couple of turns that let you switch and not get your pokemons speed cut off.

Prankster Meowstic, Swampert and Emolga did the job for me... Also Misdreavus w/ Perish song + Mean Look was helpful