Castlevania: Circle of the Moon, known in Japan as Akumajō Dracula: Circle of the Moon (悪魔城ドラキュラ Circle of the Moon Akumajō Dorakyura Circle of the Moon?, lit. "Demon Castle Dracula: Circle of the Moon"), and simply as Castlevania in Europe, is an action-adventure platform game released for the Nintendo Game Boy Advance in 2001. The game was the first Castlevania game for the system. It was the last game in the franchise to bear the "Akumajō Dracula" title in Japan until Castlevania: Dawn of Sorrow was released. Subsequent entries also adopted the "Castlevania" moniker.
The year is 1830. At an old Austrian castle, the worshipers of Chaos attempted to revive the Lord of Darkness, Count Dracula. Vampire Hunter Morris Baldwin and his apprentices, Nathan Graves and Hugh Baldwin, heard of this and headed to Castlevania to stop Count Dracula's resurrection and restoration of power. However, they arrived a few seconds too late and Camilla, a minion of Count Dracula, started the rite to revive her master.
In order for Dracula to regain his former power, he would need to wait until the full moon ritual was completed. Before the group could fight Dracula and reseal him, Dracula destroyed the floor under Nathan and Hugh, causing them to plummet down a long shaft, leaving Morris alone with Dracula and Camilla. Fortunately, Nathan and Hugh survived the fall. Hugh ran off to save his father after telling Nathan to leave the castle. Nathan decided not to, as he too wanted to ensure that his master was safe. He then explored the large castle, fighting Dracula's minions along the way.
After fighting Camilla, Nathan learned that Hugh was possessed by Dracula after the vampire exploited his desire to become more powerful than Nathan. He wanted to prove that he was superior to Nathan so Morris would bestow the Hunter Whip to him instead of Nathan. When Nathan defeated him, Hugh came to his senses and leaves to find Morris.
Nathan arrived at the ceremonial room to vanquish Dracula and save his teacher from being sacrificed in the full moon ritual. While he fought Dracula, Hugh freed Morris and together they escaped the castle, leaving Nathan to finish vanquishing Dracula. He succeeds in beating Dracula's ultimate form. Before he was sealed, Dracula stated "It is a wasted effort. I will never be truly gone. So long as there is darkness and desire in the soul of man, I will continue to be revived". Nathan replied, "And we will be there to stop you. You can bet on that". Dracula dies and the castle crumbles. Nathan then leaves to continue his training with Morris and Hugh.
The gameplay in Circle of the Moon is similar to that of other post-Symphony of the Night Castlevania titles, in which the player must explore a gigantic castle filled with undead enemies and evil aberrations in a non-linear fashion. Generic enemies defeated by the player drop useful items and equipment, and also provide Experience points which increase the player character's power. Boss enemies provide plot progression, and their defeat allows the player to acquire new abilities such as a double-jump with which to progress further in the game, the only downside in boss battles is that Magic Crystals do not appear to replenish the player's HP and MP after the fight.
The game is based around the classic Castlevania action style. The main character, Nathan, uses a whip to attack the enemies, alongside the classic side weapons: Axe, Cross, Holy Water, Knife and Stopwatch. One of these sub-weapons may be carried at any time by the player, draining a supply of "Hearts" when used. In addition, the player may boost their character's statistics through equipping items such as armor. These statistics are Strength, which determines physical attack power, Defense, which determines resilience to damage, Intelligence, which determines potency of magic and the Magic Point (MP) recovery speed, and Luck, which modifies the frequency with which items are dropped by enemies.
Unique to this game is its DSS (Dual Set-Up System) for magic, based around magic cards. This gameplay mechanic allows the player to unleash dozens of interesting abilities via combinations of two different magic cards: one Action card and one Attribute card. For example, the player can combine the "Mercury Card" (Action card with the power of whip enhancement) with the "Salamander Card" (Attribute card with the power of fire), obtaining a fire elemental whip attack as a result. Each of these cards is dropped by certain enemies, with a probability based on the player character's "luck" statistic, thus adding another search element. Use of DSS cards drains the player's supply of MP.
Compared to the other Metroidvania-styled games with RPG mechanics, Circle of the Moon does not feature a shop. Therefore, the player cannot sell any of the acquired equipment, nor be able to accumulate gold.
This is also the only game wherein the player's base statistics (STR, INT, LCK) are set to three digits (100 each) from the start.
The Battle Arena is an optional bonus area in the castle, consisting of 17 rooms. Each room contains a selection of standard enemies which must be defeated for the player to exit; however, the Dual Set-Up System (DSS) is unavailable, with the player's MP dropping to zero as soon as they enter the Arena (although it's possible to use magic in small bursts by constantly using MP recovery items). Each room usually contains a tougher selection of enemies than the last. While completing the Arena as a whole is a stiff challenge, the player can leave the Arena between certain rooms, making the area ideal for gaining Experience.
Completing the entire battle arena grants the player 291,582 experience points in total from enemies defeated, and the Shinning Armor, an armor plate that significantly increases the player's DEF, with minor upgrades to STR, INT and LCK.
There are also two DSS cards which can only be obtained from enemies in the arena: the Black Dog and the Unicorn cards.