The Aquila's B hold is for leaving an enemy apart for example a Rage, while you fight others. The witch (blue bubble girl) what I do is when she spawns her spears I switch to Osiris and hold B which reflects them back, then I demon pull her and trinity smash. If you are in a place with walls and corners try to get her in the corner so you can do the full smash.
Mundus is a joke, all I did was angel boost left to right and trinity smash him, but Mundus Spawn that I hate. I combine the parrying his punch and hitting his third arm with an Aerial Flush and when Lilith comes out I use Devil Trigger.