Breeding occurs when you select the Breeding Tree and choose a male creature and a female creature to produce another creature. To breed your critters, you need a Breeding Tree, which you first purchase in the Tutorial play.To level up the Breeding Tree, you must select it, click "Upgrade", and possess the necessary materials, which include having 10 Wood, 10 Stone and 25 Magic. When you upgrade your Tree, you increase the Breeding Power, which increases your chances of producing ultra-rare creatures. The Breeding Power of each individual animal is increased with feeding and leveling up. Feed your animals often to increase their Power, so you can produce ultra-rare creatures.
When a breeding in the Breeding Tree is completed, an egg arrives at the Hatchery. The eggs all resemble what creature they will produce, and they each have different incubation durations.
To find a table of possible breeding outcomes, go to the breeding combinations page. Note that some combinations have more than one outcome- this is because the Breeding Power of both your Breeding Tree and creature influences what the cross produces.