Get something with a move to get rid of that toxic air.
If Driftloon can do it then great, I don't use driftloon tho so I don't know.
Anything psychic eats him if you got that toxin out of the air. I had meowstic with charge beam so I was having a happy day my second battle with him. First one came down to 1 pokemon each </3 First time I lost to a gym leader in this game.
It was a repeating trend after that, prepare for trouble because the gyms don't get any easier. Except for Shade. Shade is baby food.