The fantastic Castlevania games were not the only games being censored for the release outside of Japan. Castlevania 3 for the NES console was modified for the US release. This version was also used for the international market, as for example Europe.
Side note: Castlevania 1 and 2 have not been censored!

Christian symbols, enemies were repainted/modified in their coloring.

The comparison was done between the international version for the NES and the uncensored Japanese NES version

(left: Uncensored Japanese Version, right: US censored Version)

The glow of the cross has been removed.

During the intro, when the story is laid out, the threatening dark clouds have mostly been removed, the sky looks clearer.

On the first level, a female statue was dressed up to hide nudity.

The enemy has been modified (see red circle).

The color of the end boss has been modified, probably to make it look less diabolical.

In Castlevania 3 the player has the option to get "friends", which then become playable characters. You have to fight them first and after having disenchanted them, there is the option to make them join you or not. Upon a YES, the player got a kiss on the hand from the new friend, which looked more like a handshake in the censored version