Let's discuss ideas for bosses! One of the things I looked forward to in Castlevania was the next boss because I always wanted to see something creepy or crazy.
Some ideas off the top of my head:
-Dracula - okay so maybe not Dracula himself but a vampire along those lines would fit in extremely well
-Muscle guy - I always thought it would be cool if there was a boss that looked like a man/monster with no skin but very visible muscle. He could super strong and use intense melee attacks.
-Lava woman - In a lava area there could be a woman who is created out of lava. She could change shape with the lava like become a giant face or monster or whatever your imagination desires
-Baby dragon - there could be an optional boss that is a baby dragon and has typical dragon attacks. Despite being young, he could still be formidable and can only be fought during a small window early in the game. Should the player skip the boss and avoid it, they can later fight it post game as an adult dragon and be much stronger. What a twist!
That's all I got atm. I'm going to bed.