fictional animal vs fauna

fictional animal and fauna both are nouns.

Word	Noun	Adjective	Verb	Adverb
fictional animal	Yes	No	No	No
fauna	Yes	No	No	No

As nouns, fauna is a hypernym of fictional animal; that is, fauna is a word with a broader meaning than fictional animal:

fictional animal: animals that exist only in fiction (usually in children's stories)
fauna: a living organism characterized by voluntary movement

Other hypernyms of fictional animal include animal, animate being, beast, brute, creature.

fictional animal (noun)	fauna (noun)
animals that exist only in fiction (usually in children's stories)	a living organism characterized by voluntary movement
	all the animal life in a particular region or period