The Famicom version was on the Disk System and allowed players to save their progress. This feature was removed in the international version, and the music that accompanied the screen was removed along with it. The short, simple tune has been used in future instalments for the same purpose.

Letting the game cycle through all three demos on the start screen and then starting the game will start the first level of the game with no music. The music starts again when the music would normally change in the game, such as reaching the boss.

Although originally developed as a regular NES cartridge, Castlevania became Konami's first Famicom Disk System release when it was switched to the system Mid-development.

Completing the game and playing through for a second time, it is possible to make a number of Moaui heads appear in various locations. These Moaui heads are references to another Konami series, Gradius. These appear after:
• Standing on the moving platform of the second stage.
• Crouching atop a certain staircase in the third stage.
• Walking far to the right on the third area of the third stage.

In the third stage, right before fighting the boss, standing on a certain brick and pushing left will make a money bag appear to the left. This is odd, however, as the money bag is in a location that is inaccessible.

If the player jumps over the castle entrance without being pulled in, a money bag will pop up in front of the doorway.

The names listed in the ending credits are parodies of famous people who have ties to classic horror or monster films. They are:

Terence Fisher (Trans Fishers)
Bram Stoker (Vran Stoker)
James Bernard (James Banana)
Christoper Lee (Christopher Bee)
Bela Lugosi (Belo Lugosi)
Boris Karloff (Boris Karloffice)
Lon Chaney (Love Chaney)
Lon Chaney, Jr. (Love Chaney, Jr.)
Barbara Shelley (Barber Sherry)
Max Schreck (Max Schrecks)
Glenn Strange (Green Stranger)
Oliver Reed (Cafebar Read)
Andre Morell (Andre Moral)
John Carradine (John Candy)

Also, Simon Belmont's name was accidentally left "Simon Belmondo", his Japanese name (シモン・ベルモンド Shimon Berumondo).