Okay Rika, a Gastly can be trouble, but let's not hold back here. By the time you faint, I'll make sure you are avenged by the Pokemon I'll send out next.

Taunt Spookster until successful, then if you can, get in a Rain Dance to put out the flames. If you still have an action left, use a Shadow Ball on him

Sub:

If he dares come close to you, shock him with a Thunder Wave, but make sure that you get to use Rain Dance. Otherwise, the fire could be trouble for both you and the Pokemon I'll eventually send in your place.