The game features twenty single-player missions as well as a co-op mode that allows two players to complete the campaign together. Events on both maps happen at the same time, forcing players to divide their attention. Additionally, some missions feature no dungeon and have to be played with a fixed number of units provided. Most maps require certain goals to be achieved on this map. Unlike in the dungeon, players can select units like in other real-time strategy games and issue commands directly as well as use their skills. Units that leave the dungeon reappear in the over-world map. Each dungeon features one or more such entrances that also allow units to be sent to the world above by grabbing the units with the hand and placing them on the exit. While in dungeon building mode, units cannot be controlled directly but picked up using the hand and dropped where they should be, for example to attack heroes that have entered the dungeon through one of the entrances. In the bottom left and right corners, the two mini-maps can be seen. Thalya stands in front of a dungeon entrance. Dead Demon units will be resurrected in a lair using mana and defeated Undead units will slowly regenerate in their graveyard. While each faction offers their own technology tree, many aspects can be combined for better results: For example, heroes captured in the Undead prison can be tortured in the Demon torture chamber to switch sides and fight for the player and Undead crypts can serve to resurrect dead Horde creatures.
Even with upgrades, players can only recruit 20 units from all three factions combined as well as up to five converted heroes additionally, undead skeletons and zombies can be created from fallen heroes that do not count towards this limit. Additionally, each faction has a singular powerful titan unit that can only be hired once. The game features both neutral units and rooms, such as a treasury and farms, as well as three factions that provide their own specific advantages and disadvantages: The Horde allows the player to hire goblins, orcs and naga and provides access to training rooms and traps Demons consist of imps, arachnids and succubi and allows the player to research upgrades as well as generate mana for spells and advanced traps and The Undead faction offers banshees, vampires and lich creatures and rooms like a prison to incarcerate attacking heroes. Almost all units demand a number of comforts, including a regular wage, rooms to sleep in, food and relaxation, and will go on strike if their needs are not met. With the exception of Thalya, the player's hero unit, all other units have to be unlocked by research and hired through an in-game menu. "Evilness" is a resource generated by capturing certain places in the over-world and is needed to research stronger technologies and upgrades. Beer is brewed by Horde units in special rooms and serves to keep those units happy. Mana is generated by Demon units and is used to unleash powerful magic spells as well as revive Demon units and turn toolboxes into magic toolboxes for more powerful traps. Toolboxes are used to make traps as well as to create certain contraptions in some rooms. Gobblers are little chicken-like creatures continuously created by a farm and serve as food for creatures. To build and maintain their dungeon, five different resources are available: Gold is gained by excavating gold veins in the underground and is used to pay for rooms, units and new technologies. Additionally, the dungeon heart room stores gold and features a trap door that can be used to get rid of unwanted units. It is the primary target for attacking heroes and its destruction leads to a game over. Commands are carried out by little imp-like creatures called snots, which are constantly regenerated by the dungeon heart which is the center of the dungeon and represents the player's health. The hand is also used to designate parts of the underground for excavation and to create rooms. In dungeon building mode, the player controls the world with a hand, performing actions such as moving creatures around the map, casting spells, and interacting with specific items. The primary task is to build a dungeon, an underground lair which serves as a home to the player's units and their base of operations. Dungeons 3 is a dungeon building video game with real-time strategy elements.