Mobs can be spawned by combining a spawner controller with a spawner cage below. The size of the spawned entity determines the required cage size. The type of mob spawned is determined by the first mob to walk over the controller and can only be changed by replacing the controller. The controller collects souls and uses them to spawn the set mob, with the soul cost depending on the mob's HP. Mobs will only spawn if an empty surface is available nearby.
When a mob type is set (or when right-clicked if invalid), the spawner highlights the required size of the spawner cage below. You can also right-click the spawner to get information on the current operational state.