The game uses a third-person perspective inside enclosed rooms. Millennia must survive encounters and complete objectives by placing traps on floors, walls, and ceilings, then triggering them when enemies enter the correct positions.

Story stages typically involve several rooms and groups of enemies. Traps can be chained into combinations, allowing one effect to launch, stun, burn, freeze, or otherwise reposition a target for the next attack. Successful missions award resources used to acquire and develop additional traps.

Study enemy movement before spending traps, and begin encounters with inexpensive devices that control position. Wall and ceiling traps are especially useful after an enemy has been knocked down or launched.

Build combinations around a reliable sequence: first stop or reposition the target, then apply the stronger damage trap. Leave enough room to retreat, because several enemies can activate a setup at once. Replay completed missions to improve trap selection and resource management.