Did I just unlock an ANCIENT ARTIFACT?!

While trying to map out the RAM addresses for the US release of Castlevania on the NES, I found a variable that kept getting checked only when I used a subweapon. The only time byte $015C got written to was when the Rosary (the cross-shaped item that flashes and kills everything on screen) stopped flashing the screen, but it was always just overwriting the same value of #00. Was this scrapped code? 

It only took me 30 seconds to search the program for another write to that address. The code wrote a value of #0f whenever subweapon #0a was used. That was simple! So I plugged in #0a for Simon's subweapon. Lo and behold, subweapon #0a is....

THE ROSARY?!?!!!

Rosary as a subweapon

It requires 5 hearts to use. The RAM address in question is used to prevent any subweapons from being used while the screen is flashing -- a pointless endeavor, because address #015D is also set and decremented when the Rosary is used.