There are a few ways to improve your chances of getting a rare creature. Save Gems to purchase new Creature Eggs. You will be guaranteed at least a three-star creature. Spend Dragon Fangs on the "Shallow" egg category. However, the maximum rarity available is is a three-star creature, with mostly poor ones otherwise. Participate in the limited time events to get the chance to win prizes that include rare creatures. Log in regularly to claim rewards awarded for frequent game play. Level your creatures to their maximum level first, then Evolve them to get a better star version.