Castlevania: Harmony of Despair brings together a cast of protagonists from previous games in the series with the classic 2D platformer gameplay. The focus is on cooperative gameplay with up to six vampire hunters workings towards the same goal of eventually destroying the citadel Castlevania. This is similar to the Boss Rush mode from previous games, but there is also a Versus mode to play against each other, based on points. Additionally the game can be played alone, in a singleplayer story mode. It consists of six large maps that can be browsed while playing. There are three different zoom levels (not pausing the game) and even though the closest one is the only suited to play, the others allow you to view the entire level layout in a single screen to plan a path and find out where the treasure is. At the end of each level is a boss that needs to be defeated and familiar villains such as Gergoth, Dullahan, Puppet Master, Death, and Menace make a return. Bosses are sometimes able to attack players before reaching the end area. Multiple players start in different parts of the level and act independently, but since each character has a different set of skills, it is possible to help each other by dousing fire to clear a passage, or pulling a lever to raise a platform for another player.
Just like the previous games in the series there is a focus on RPG elements. For instance, using a weapon often raises the skill for it, making it more effective over time. The protagonists have health and magic bars, and when fighting enemies the damage dealt is shown as a floating number. Players can raid treasure chests and collect loot to equip both offensive and defensive gear, as well as gain bonuses for individual skills. Often equipping mid-game is only possible when a magic book called The Grimoire is located. The character’s main statistics are divided into seven categories: ATK, DEF, STR, CON, INT, MND and LCK. There is however no experience points system, unlike some of the earlier games, and it entirely based on better items and weapons. Money gathered in a level is carried over, even when dying. When playing together items in individually looted chests are provided to all players. When one of them perishes, a grave appears where the character died and he can continue fighting in skeleton form, with limited abilities. Other players can use Water of Life to revive a character, but when all characters are in skeleton form, the game is over. Levels also need to be completed in less than 30 minutes. A number of phrases are available to pass on a message to the players.
All characters share a number of abilities combined with a few unique hunter skills and a personal skill. They are able to double jump, use two types of attacks, back dash, and use spells. Other elements are only available to specific characters. Alucard can change forms while Shanoa uses glyphs near a magnet to attach to it, build up tension, and then spring away at rocket speed. Enemy abilities are sometimes released in spirit form and can be used by Soma, based on three categories: Bullets (collect up to four bullet souls), Guardians (used as a personal skill), and Enchantment (activated immediately when it is equipped). Spells are collected though magic scrolls and there are four types of dark magic, while for Jonathan Morris martial arts scrolls provide new physical abilities. Magic is also acquired by Charlotte Aulin using the book of binding to lock projectiles and enemy spells, or by absorbing the magical sigils that appear sometimes when enemies use magic.
Initially five characters are available, with six more available through downloadable content. In multiplayer eight different palettes are provided to change the appearance of identical ones. The characters available are:
- Alucard (from Castlevania: Symphony of the Night)
- Charlotte Aulin (from Castlevania: Portrait of Ruin)
- Shanoa (from Castlevania: Order of Ecclesia)
- Soma Cruz (from Castlevania: Aria of Sorrow)
- Jonathan Morris (from Castlevania: Portrait of Ruin)
- (DLC) Julius Belmont (from Castlevania: Aria of Sorrow)
- (DLC) Yoko Belnades (from Castlevania: Dawn of Sorrow)
- (DLC) Richter Belmont (from Akumajō Dracula X: Chi no Rondo)
- (DLC) Maria Renard (from Akumajō Dracula X: Chi no Rondo)
- (DLC) Simon Belmont (from Castlevania)
- (DLC) Getsu Fuma (from Getsu Fūma Den)
The PlayStation 3 release includes Julius Belmont, Yoko Belnades, and the stage Love, Desire, Situation Dire at no additional charge. It also includes a single-screen offline multiplayer mode and minor balance changes.
