Not the greatest coverage
Only hits 3 types super-effectively. May be good but not good enough.
Also, even though it is not common, it's quite good.
High power and decent accuracy but not recommended.
Heck, even special sets aren't used much. Mostly mixed sets.
Here's a good mixed mega set:
Salamence @ Salamencite
EVs: 200 Atk/252 Spd/56 Sp.atk
-Dragon Dance/Roost/Tailwind/Zen Headbutt
The role here is to be a mixed attacker obviously xD idk why I just stated the obvious.
So anyways, that Hyper Voice is gonna hurt even with only 56 sp.atk EVs invested. Last slot is your choice.
Roost is to last longer.
Dragon Dance is to set up and hopefully become a threat.
Tailwind is for support.
Zen Headbutt is a filler.
Hope I helped!
-It's a secret!