Castlevania III's Japanese counterpart, Akumajou Densetsu, features a microprocessor chip in the cartridge, named the Konami VRC6. Aside from a few scrolling enhancements, the chip also adds three audio channels to the Famicom's existing five. These channels could provide more extensive and different kinds of sounds than the internal 2A03 chip. Since the international NES does not support the VRC6 expansion, a different chip was used, the Nintendo Memory Management Controller 5 (MMC5). This expansion, however, only adds two clone pulse wave channels rather than the VRC6's two different pulse waves and a sawtooth wave. As such, the NES version of Castlevania III does not feature the advanced sound that is in Akumajou Densetsu.

The international version of the game has many graphical differences when compared to the Japanese version. These include the cross in the intro losing its beams, the prologue clouds becoming static and the character name input screen's statues gaining robes.