The enemies I would like added are from a certain card game that konami produces.
Now it is yu-gi-oh, but the creatures I have in mind go hand in hand with one of the levels in the cv-verse los or not.
Now we all know about the crystal castle right?
Castlevania Belmont's Revenge Stage 01 Crystal Castle (No Damage, Subweapons, Upgrades)Sweet...
Now these monster are called the crystal beast

Now how could the crystal beast fit into the cv verse? Well let's say that the crystal beast when all together can bring out a powerful beast, but in order to do that one must beat all the crystal beast in their area in the crystal castle and when a beast is defeated they turn into a gem like this

And when all the gems are together in say an altar for the seven beast.
They summon the hidden monster that's just freakishly powerful

And then you have to fight this rainbow of a dragon. It would be a great way to reintroduce the crystal castle back
and even give it a little back story to the castle.