Full Mojo Rampage is a roguelike action game with a voodoo theme. The game has randomized environments, enemies, and items, as well as permadeath, but certain game elements carry over across sessions, such as unlocks, a global level achieved through experience, and the collected currency. The main character is a voodoo student who aims to please the loas, the voodoo gods. At the start of the game the player chooses one of the eight available loas (unlocked gradually) that each have different statistics based on a passive ability and two types of spells. The player character has a global level regardless of the chosen loa, based on health, damage, movement speed and attack speed. Through multiple sessions experience is gained to level up the global level. With each new level any of the four main statistics can be upgraded. With every new session the enemies match the player's level.
There are four main quest levels with multiple areas for each, a daily random quest, a 30-round survival mode and an unlimited survival mode. The quest levels need to be unlocked gradually. Once an entire quest is completed, the next one becomes available and for the completed one a new difficulty level can be selected, with more than five difficulty levels available. A single quest consists of a randomized sequence of areas that needs to be completed in a single session, with fixed bosses. Each quest has its own environments and enemies. In addition there are optional, random rooms such as altar rooms, mojo mixer rooms, dungeons, riddles, shops and treasure rooms.
The character can be moved around and can shoot a magic bolt in any direction. Next to this primary weapon with unlimited ammo and the passive ability based on the chosen loa, two spells can be used at any moment, but with recharge time. These are also tied to the chosen loa and include for instance a dodge roll, a homing fireball, a circle where the fire rate is increased, a spell that slows enemies down etc. There are slots at the bottom of the screen for equipment and inventory. Mojos are special items that are stored as abilities in the equipment slots. They are randomized for each session and are picked up as loot during level. Each item has different effects, such as more health, better health recovery or recovery through kills, a fasting firing rate or movement speed, more damage etc. As there is only limited room, the player often needs to swap them. In mojo mixer rooms certain types of mojo can be combined into a single item, carrying the benefits of both individual ones. The equipment slots hold health potions, one-time use or rechargable items and more. Through certain items the slots for equipment and inventory can be increased. The levels also contain various staffs, temporary powerful weapons with limited ammo. Only one of those can be carried at any time and once depleted it is removed. It is however possible to temporarily store it in the inventory instead. By killing a certain amount of enemies a rampage meter is filled. When full, a power-up spawns with a different effect for each type of loa.
Quest areas usually have an objective to collect a certain amount of objects such as flowers, bottles or bones before the exit is opened. Sometimes a number of portals needs to be destroyed. There is a mini-map, but initially the level is shrouded until a part is explored. Next to enemies there are treasure chests, destructible objects, secrets, and different types of rooms. Altar rooms offer an enhancement or a risky power-up, such as trading health for damage. In shop rooms new items can be acquired in exchange for gold, the main currency, and equipped ones can be sold. It is also possible to donate money for a chance to receive a prize. Treasure rooms hold powerful items. A quest area generally consists of a single, large environment. The other types of rooms, such as dungeons with an emphasis on avoiding traps, are only accessible as separate levels on the main map.
While playing the character collects gold and medals. These are kept even when dying. The currencies are used to unlock new loas, masks, and additional perks. Certain masks only become available after locating a scroll that contains a voodoo code. These codes can be entered in a separate screen in the main menu. By unlocking pins in-game, up to three permanent bonuses can be chosen from the character selection screen before starting the game. These perks provide additional health, poison damage, a chance of blocking etc. Each pin can be upgraded several times. In addition a one-time seal can be bought as well to receive even more benefits. Next to the single-player game, multiplayer is supported both offline and online with cooperative games for up to four players, and online PvP games for up to eight players.