Unused Stage Select
Why, you ask, would a game that features a password system need a "Stage Select" mode? The developers of Super Castlevania IV thought the same, so they after cooking up a stage-select option (perhaps for their own convenience) hid it away in the annals of the game's cartridge. Still, it might be worth your time to unlock it, using a Game Genie or Pro Action Replay, if your intent is to access specific areas of a stage, which this mode will allow you to do. The particularly long passwords are show below:
Pro Action Replay:
This information is credited to http://tcrf.net and was sent in by Christopher M.