There is a very Large secret in the final section of Super Castlevania IV. It is so well hidden, you would not even know of its exsistance!
When you enter the famous final stairway to ascend to Dracula's chamber, stop. Go over to the edge of the walkway by the stairs. No here is where you need a bit of faith...jump out over the chasm. Whoa heck no! Are you nuts! Yea got that from a couple of people too. No seriously jump out, and see what happens. I'll wait...

If you open your eyes back up, you will notice you are standing seemingly in mid-air. Now carefully, go to the left, holding the downbutton too. You will soon begin descending a set of invisible stairs. Right under the Castle Keep, the screen will flash, and then you will get a big suprise. You will recieve 99 hearts, aweapon upgrade (If you need one), a Double Shot followed by a Triple, and a Boomerang. Now if that is not simply frickin awesome, I do not know what is!
Once you have obtained you great bounty, head back up the invisible stairs, and hop back over to the platform. Remember that the invisible platform at the top is only two blocks wide. It is very easy to fall off.
This should greatly assist you in your final fight with Dracula