I think your HUD looks too big, comparing to Castlevania NES. In the latter, you can see many info in the HUD without sacrificing readability. IOW reduce the text, icon and HP size to allow more info in the HUD. That includes boss's HP bar.
That being said, it looks good. I can imagine on what's happening here.
Oh if you're going to post updated mockup next time, please show the weapon from both characters to see how much screen is filled with their weapons.