When using Ebony & Ivory and the shotgun, you can shoot the shotgun faster by firing, switching to Ebony & Ivory with (L2 default) firing once or twice with them, then switching back to the shotgun. If timed correctly, you can fire the shotgun as if it were one of your pistols!
You can glide while in demon form by having the Rebellion equipped. (Hold) R1 + X to glide. This move will not appear in the library, but is automatically learned. And you can purchase the Air Raid maneuver for the Nevan weapon!
On mission 19 have a second controller plugged into your ps2 so after you hit arkham a few times you should see a cutscene as soon as You see the cutscene grab your second controller and press start and if he does not move after 2 seconds you have done it.