Castlevania: Circle of the Moon,[a] titled simply Castlevania in PAL regions, is a platform video game created by Konami for the Game Boy Advance. Published as a launch title in 2001, Circle of the Moon belongs to Konami's Castlevania video game series, the premise of which centers on the eternal conflict between the vampire hunters of the Belmont clan and the vampire Dracula. The game sold one million copies worldwide and was acclaimed by critics. The events of its plot were retconned by former Castlevania producer Koji Igarashi, a move which was met with some criticism.
The game was re-released as a part of the Castlevania Advance Collection on September 23, 2021, for the Nintendo Switch, PlayStation 4, Xbox One and Windows. It was bundled alongside Castlevania: Harmony of Dissonance, Castlevania: Aria of Sorrow, and Castlevania: Dracula X.
Circle of the Moon makes use of a 2D side-scrolling style of gameplay, similar to many of the previous Castlevania video games.[3] The objective of Circle of the Moon is to lead player character Nathan Graves through a monster-filled castle as he searches for his kidnapped mentor.[4] Like many of the previous Castlevania protagonists, Nathan uses a whip to attack and defeat enemies, alongside secondary weapons—an axe, cross, holy water, dagger and stopwatch—only one of which may be carried at any time by the player.[4] Hearts, typically found within candles, are used as ammunition for subweapons, with some using more than others.[3] Circle of the Moon follows a nonlinear style of gameplay: at the beginning of the game, Nathan can only traverse certain areas of the castle; by obtaining various abilities, such as becoming able to run, double jump, and wall kick, he gradually explores the castle.[4] He will also encounter rooms with the ability to teleport him across portions of the castle and rooms which will restore his health and allow the player to save their progress in the game.[3] The game automatically updates the castle map to reflect Nathan's progress through it.[4]
Circle of the Moon incorporates role-playing elements.[5] Nathan possesses various statistics: hit points, the amount of damage he can withstand before dying; magic points, how often he can cast a magical attack; strength, the power of his physical attack; defense, his resilience to damage inflicted by the monsters; intelligence, the recovery speed of magic points; and luck, the frequency with which items are dropped by enemies.[3] Defeated enemies drop various items and equipment, and provide experience points; after reaching a predetermined number of experience points, Nathan will level up, and his statistics will improve.[4] The defeat of boss enemies allows the player to acquire new abilities to progress further in the game.[3]
Unique to Circle of the Moon is the Dual Set-up System (DSS), based on magic cards found throughout the game that belong to one of two categories: Action and Attribute.[5] Each of the ten Action card takes its name from one of the gods and goddesses from Roman mythology, and determines the type of magic being performed, while the ten Attribute cards take their names from creatures from Greek and Roman mythology, and add an effect to the magic.[3][5] To produce a magical effect, the player combines one card from each of the two categories, for a total of one hundred different combinations.[5] In "The Battle Arena"—an optional area of the castle which consists of seventeen rooms filled with stronger versions of monsters found elsewhere in the castle—Nathan's supply of mind points is drained, causing the DSS cards to become temporarily unusable.[6]