Equipping a special obtainable item called the "Bear Ring" and activating the Pluto & Black Dog combo will change the main character, Nathan, into a cartoon bear known as BearTank from the game Rakugakids.

All the "DSS Action cards" are named after Roman gods and goddesses except for 'Uranus' which uses it's Greek name. Uranus is the Greek name of the God of the Heavens, the Roman name of this God is 'Ouranos'.

A preview demo for the game was shown off at the Autumn 2000 Tokyo Game Show. During this preview, GameSpot and IGN both reported that there would be two playable characters, Nathan Graves and Hugh Baldwin. However, the demo only featured Nathan Graves as a playable character with no option for a second character present. No screenshots or descriptions of Hugh Baldwin in this demo are known to exist, and he was ultimately not playable in the final release. It is unknown if a playable Hugh Baldwin was cut before release, or if the press were simply mistaken.

For unknown reasons, the European release of Castlevania: Circle of the Moon had its title shortened to Castlevania.