Riddle is a song originally composed by Konami Kukeiha Club for Castlevania III: Dracula's Curse. It is the background theme for Block 9.
A 2008 version arranged by Yasuhiro Ichihashi appeared later in Castlevania: Order of Ecclesia. It is the background theme for the Training Hall and the Large Cavern.
Most recently, it was used as the background theme for Dracula's final form in Castlevania: The Adventure ReBirth.