After completing a creature, its habitat unlocks. Now, once a creature’s habitat has been unlocked, you’ll receive a Mystic Isle jewel per creature per day. These jewels can be used to get Mystic Isle decorations and boosts (which will help you advance across the Main Island and Paradise Cove).
Completing the same creatures – for example, multiple owls – is beneficial, too. For every additional final creature you merge (up to 10 per habitat!), one hour will be knocked off the corresponding habitat’s daily countdown timer. You’ll receive your jewels faster.
The type of jewel you receive also corresponds to the creature’s rarity. For example, since an owl is a Common Creature, its habitat would produce Common Jewels. As a Legendary creature, the T-Rex’s habitat would produce Legendary Jewels.