Accelgor is a very speedy Pokémon with a good sp.atk. A modest nature would be good for him. His defenses are bad, so you could go with choice specs or a life orb if you think you can OHKO other things, or a focus sash to actually live a little bit. Salamence is very strong with a mega evolution. If you are mega evolving him, his ability aerilate makes his normal moves flying and gives them a boost and power, which is incredible. If you are mega evolving scizor, then try to get his hidden ability, moxie. It
boosts his attack upon fainting a Pokémon. Hope this helps!