The Celestial Beasts have a state of being called Core Forms. These are the the Beasts at their "weakest" and core of their beings. Although they can take these forms at any time, they revert into them if their manapool gets critically low or they take too much damage to reserve power. While in these forms, each of the Beasts are at there "base" as an individual, and are more likely to act in ways that resemble ways near the beginning of their creation. They are still able to cast spells and carry out primary functions, but at a much lesser degree.