The energy from Salamence's Mega Evolution is focused on its wings. Its two wings fuse together, becoming a single huge wing in a crescent shape. When flying at high speeds, this wing becomes a great blade, slicing through anything loitering in Mega Salamence's way.
When it Mega Evolves, its Defense stat soars. With its already high stats climbing even higher, this becomes an even more promising Pokémon than before. Its Aerilate Ability also makes Normal-type moves into Flying-type moves, increasing the ways that Mega Salamence can battle.