5: Dmitrii(DoS) and Doppelganger(PoR). If you give them some good equipment/souls that is. 4: Blackmore(or Blackloth, or whatever his name is) 3: Dracula(without rapidus fio that is) 2: Albus(OoE) 1: Dullehah(PoR) and Death(PoR). Unlike the above bosses, these guys can't be defeated in a cheap and easy way the first time you face them.
Even with those pits, Dracula wasn't that hard in that game. Despite the fact that the fight against Dracula from the original Castlevania was very similar but without the pits, it was much harder simply because you had to time your whip lashes perfectly to avoid getting hit by his fireballs and 4 hits killed you while it took like 20 to kill him. I remeber beating Dracula X way back when even just reaching Dracula in the original Castlevania still seemed impossible to me.
Also, lol at Castleroid bosses making it into lists. Any of the bosses in the later levels of the 3 NES games was way harder than any Castleroid boss. There was no sissy equipment or items back then. Or hyper or even double jumps to fix screwups. Just you, your whip, and whatever sub-weapon you had.
And even more lol at Brachyura being first in the OP's list.
You're reading the secret phantom signature. Everyone else sees this sig as some stupid reference. Congratulations! You have 6 days left to live.