Minecraft wiki entry for Creating_custom_entity_add-ons, associated text: First, make sure to define the identifier for your custom entity (prefix can be anything), then if you want your entity to have a spawn egg in creative inventory, set "is_spawnable" to true. Set "is_summonable" to false to make it not summonable using /summon commands. For more information about entity component add-ons see: Entity JSON Documentation