Simple, you get a Mob Selector(Material: Bone) in your Inventory with the name "Mob Chooser" When you will click on it its will open for you a Monsters and Animals Inventory inside the inventory will be 2 category Animals and Monsters when you will click one of those category its will open you another inventory what inside it will be Monsters eggs that when you click on it its will Spawn Mob what you wish for.
