Monster Spawner is an object unobtainable by players through normal means. This item's information is present in the game files, but not intended by developers to be in players' possession.
When placed correctly, the Monster Spawner will spawn a single monster that will function like any naturally found monster in game. It will respond to the player and events (such as monster attacks) as normal.
Upon placing of the monster, the spawner will automatically summon 5 quadruped type monsters. Picking up and re-placing the spawner will summon 5 more monsters. This object was disabled to make way for the tenant system in Pleased Giraffe.
As of Cheerful Giraffe they have been reworked an placed in several Dungeons and in the Great Sovereign Temple. Despite being found in these dungeons, the Monster Spawner will immediately disappear if someone attempts to mine it.