Zombie Spawn Egg item in Minecraft

What it does

Spawn eggs cannot be crafted or found in survival: take them from the creative inventory or get them with the /give command. Use one on a block and the mob appears on it; aquatic eggs can also be used directly on water.

Used on an adult of the same species, an egg spawns a baby instead. Used on a monster spawner or a trial spawner in creative mode, it changes the mob that spawner produces. An egg renamed on an anvil gives its name to the mob it spawns, and a dispenser can use spawn eggs too, which map makers rely on.