If you use a spawn egg that has custom EntityTag data set, usually it will summon a mob with that entity data. However, if you use the spawn egg on an adult mob, it will just spawn the baby variant of that mob without any of the custom entity data.
- Give yourself a spawn egg with custom NBT:
- Use the spawn egg on a block. This will summon a sheep named "jeb_"
- Use the spawn egg while looking at the sheep you just summoned
A new baby sheep is summoned. The baby sheep does not have a custom name.
A new baby sheep is summoned. The baby sheep is named "jeb_".