Skarm

If you buy a soul candle in 7th street then go back to where luna was held by the cultist, you can get a litwick (which evolves into chandelure) any other pokemon that learns acid rain/smog/clear smog works too, just be carefull with the gardevoir, which can pop your balloon and thus make you die to earthquake.

I used a clear smog x2 chandelure (on a balloon to avoid earthquake) to change the terrain, with a steel type for bait/support on first turn. Then a salazzle to sweep with fire or venoshocks (watch out not to combust the field on accident). By the time he used defog/tailwind (dont remember which) my other mons were able to finish it.