Castle Crashers is a side-scrolling, beat em up which incorporates a small number of role-playing game elements. After selecting a character, the player then selects a starting level through a graph-like world map; once the player completes a level, they may then opt to move or revisit that level any time. Other levels include shops where the player can buy items for healing, attacking, or defense using coins gained from defeated foes, and arena levels where the player can take on challenges to unlock additional characters. During cooperative gameplay arenas turn into a player vs player match. At the end of each section players battle a boss character to free a princess. If two or more players exist they must battle each other after defeating the boss to compete for the princess's kiss.
In each level, the player can use a number of melee attacks and combination attacks. Each character also has a unique magical ability in order to defeat foes. The player has a health meter that, if drained from enemy attacks, will cause the character to fall in battle. If the player is playing alone, this ends the level and the player will have to start it over. However in cooperative multiplayer any of the other players may attempt to revive the downed character. The player's magic level is also tracked by a meter and regenerates over time. Numerous weapons can be found in the game, each that have various effects to the character's attributes when equipped. There are also animal companions that can be found that may help out in battle, improve the character's attributes, or provide another special ability such as gaining more treasure from defeated foes.
After a player damages an enemy, they gain experience points, eventually gaining the player a new level. Each level gained allows the player to allocate points towards four basic attributes to improve that character in combat. Certain level advances also grant new combination attacks. Progress in experience and game completion is tracked for each of the playable characters separately. New playable characters can be earned by completing the game with a new character, or through downloadable characters from xbox live marketplace such as the titular character from Alien hominid
After a player completes the main game, they then unlock a much harder difficulty setting known as Insane Mode which pits the player against far tougher opponents who deal far more damage. The game supports up to four player co-op, either locally or through Xbox Live The game progression in terms of what levels are unlocked is defined by the hosting player; however, each player can continue to gain levels and acquire wealth, weapons, and animal orbs as they progress with the rest of the party.
Each version of the game features two minigames In Arena players attempt to survive through several waves of enemies. The Xbox 360 version features All You Can Quaff, a button-mashing contest between all players to attempt to eat as much food as possible. The PlayStation 3 version features a game of Volleyball playable with up to 4 players and 4 AI characters.