In Crystal Mines II, you operate a robot going through the abandoned crystal mines, picking up crystals and avoiding the underground demons that inhabit the mine. Mine levels are completed when a crystal quota is reached, however the quota is usually not the entire level so bonus points can be obtained by finding additional crystals. Like Boulder Dash, gravity is a factor and affects any boulders, crystals, etc. so they can be used as weapons against demons. There are also deceptive elements, such as "Dormant" demons that look like boulders, that add to the challenge. Finally, the robot has weapons that can be used to eliminate certain obstacles.