From the wiki: Mutants also can not take the form of the following creatures: Chimera, Fate Egg, Devonian Dragon, Scarab, and Immortal.
Is this all accurate? I understand Chimera and Scarab, and sort of get Fate Egg and Immortal.
But why in the world can Devonian Dragons not be mutants? In terms of base cards, they have exactly the same stats and cost as Black Dragon, Purple Dragon and Bone Dragon.