Re: Salamence Lead
Azelf leads tend to be more interested in setting up screens, as the standard lead on heavy-offense teams. Azelf is faster than any non-scarfed Mence, and once it gets the Reflect up your 2HKO is gone. HO teams usually intend to sacrifice their lead Azelf anyway.
Explosion not KOing Mence may give people a surprise, but with so little investment in your offences, and the Azelf leads you're targeting having already set up screens, you won't be able to threaten your opponent back.
Of course this is all theory. You should test your set out. It may actually work well. But I'd bet if it does, it's usually against leads other than Azelf.