Keys unlock locked treasure chests and doors in various Castlevania games. They were first introduced in Vampire Killer, where a yellow key opens chests, while a white key opens a locked door. They returned in Castlevania: Rondo of Blood and Castlevania: Dracula X, where they take the place of a Sub-Weapon and can even be used to attack an enemy (item crash at least causes temporary invulnerability if it misses its target). They unlock doors where maidens have been locked up in. Keys of all types appeared in later Castlevania games. Sub-weapon replacing keys returned in Castlevania: The Adventure Rebirth and are used to take alternate paths through the stages.