LOL, my Dusclops would humiliate that. The one here that is used has all that -Flamethrowerm and +Rest Making it hard to take down soley with my Dusclops.... If that is its moveset, try my Clops. It is a tad time consuming, but Protect, Willo until it is burned, then Protect, DT, P, DT, repeat P/DT, will widdle it to no HP in no time. Also it will have to struggle if it doesnt KO from Burn. Toxic works well too, I just chose Burn over Poison (fewer Pokemon cant be burned).
Also, maybe a Salamance or Gyrados. Elimanates Flamethrower and EQ from being used, lowers Slakings attack a bit, then teach Protect.