"Right, Fang, we're at a disadvantage because of the weather, but let's show this not-so-friendly ghost what we're made of!
Start off with a Shadow Claw, with it's increased chance for a crit! Then Dig underground to avoid seeing and hearing the yawn! Too bad he's levitating, but we can't afford to go to sleep! Finally, finish up by Waterfalling straight through the will-o-wisp into Casper. The water you surround yourself with should extinguish the flames. If the ref decides this is improbable, use water gun to put out the flames instead.