Source: Bestiary 2, pg(s). 54
A chaos beast resembles a horrid mass of eyes, teeth, tentacles, stingers, claws, and so on, constantly twisting upon itself and reshaping into new forms.
Chaos beasts are formed from the majority of the shapeless petitioners in the Maelstrom, who neither petitioned a protean chorus to be transformed into one of them, nor qualified for transformation into a valkyrie or einherji. The chaos beast's attack curses its foe with an amorphous body that is constantly melting, flowing, writhing, and boiling. Chaos beasts are resistant to transmutation effects, quickly reverting to its normal form if forcibly transformed.