I need one more pokemon. advice please?

Mega Haxorus, Delta Hydriegon, Delta Scizor, Greninja, Volcarona. who should my last mon be?

for what i see a pokemon that could help your team is (in my opinion) a physical ghost type pokemon or physical eletric type pokemon

Delta Typhlosion maybe? Gengar? Do they have to be physical

no they dont both of those are preety good i just sugested a physical because you have 2 physical pokemon and 3 special

Another question, are the elite four teams level scaled to your team if you know?

Yes, although the minimum level the Elite 4 will go is around level 85.

Delta gallade