Oh, I didn't know you were trying to do that
If the gym was still under normal conditions then I believe that Pecha would almost be able to sweep the whole thing but we are in chaos world here. Any pokemon belonging to a local gyms type could be hanging around inside and they would not be push overs except maybe to a type that they are weak against.
Having said that, a risky gym challenge might be allowed if the battle is spectacular enough and the hero pokemon just barely wins in the end. (but only if everyone does not overdo it, no one expects us to be easily taking down gyms with a huge type disadvantage)
Although I do like how you made Pecha show major guts by attempting it.