Monster Spawner

Mob Spawners are blocks with a transparent blue lattice structure found in dungeons. Inside it are flames representing magic and a miniature model of the mob it spawns, continuously spinning and getting faster until the mob spawns in the area around the cage. Mobs will never stop spawning from it; this has lead to many contraptions designed to kill whatever drops from it, such as large pits or lava wells, abusing the spawning mechanic.

When found inside dungeons naturally, they will either spawn Spiders, Skeletons, or Zombies. Although you can no longer destroy them and keep them for yourself, they were originally capable of being destroyed by a pickaxe and collected for the player to place. When placed by the player, they would only spawn pigs.