Castlevania: Rondo of Blood is designed to be compatible with a Version 3.0 System Card (distinguished by the Super CD-ROM² branding instead of the CD-ROM² brand found in earlier versions). Despite this, if the player inserts a Version 1.0 or Version 2.0 System Card before bootup, the game will enter Akumajyo Dracula Peke, a hidden self-parody minigame. The title logo is deliberately misspelled (i.e. "Akumajyo" instead of "Akumajou") and written almost entirely in hirigana save for the "X" at the end, which sports furigana reading "ペケ" ("peke"); the latter is a Kansai dialect term for a wrong answer or prohibited action, riffing on the fact that the player inserted the wrong type of System Card. Upon pressing the Run button, the game will then load up "Stage X", featuring a much more cartoonish art style and a splash screen claiming that "The fated bloodline will fail without a Super CD-ROM²." Reaching the end of this stage results in Maria apologizing before text appears instructing the player to turn the game off and swap out the System Card for a Version 3.0 one.

Akumajyo Dracula Peke is retained in both Castlevania: The Dracula X Chronicles and Castlevania Requiem, complete with an English translation. However, the ending text is changed to accommodate the different methods used to unlock it in each re-release. In The Dracula X Chronicles (where it is unlocked by beating Boss Rush Normal three times, the third while having the Key sub-weapon during the Lesser Vampire fight), the text reads "Press START button to quit this game." Meanwhile, in Castlevania Requiem (where it is unlocked by inputting the Konami Code while highlighting "Options" in the main menu), it reads "Castlevania Requiem does not support extra lives codes. Press Options to quit, cheater." Both re-releases additionally rewrite the splash screen at the start of the level to say "Destiny cannot be stopped here."

In Stage 5 of Castlevania: Rondo of Blood, there is a secret passageway that can only be accessed by Maria. It leads to a white object resembling a mirror or doorway that cannot be interacted with. In the PSP remake, a Soundtrack item can be found here.

There are a large number of unused dialogue pieces in the Symphony of the Night's data, including what may be an unused ending. Many of these sound files are alternate versions of voices that are already used in the game, but extended or slightly different.

A series of clips can be found in the game's sound files, which seem to be an unfinished ending. It seems to suggest that Maria intervenes in the fight between Alucard and Richter, where she becomes possessed or transformed by Shaft. It includes both winning and losing quotes, and ends with Alucard reflecting on the apparent death of both Richter and Maria. While the PlayStation Portable and Saturn versions allows a fight with Maria, it is not under these circumstances. There are no other suggestions towards this ending, but it is assumed to be an alternate ending during the fight with Richter when not using the glasses.