basilisk vs mythical creature

basilisk and mythical creature both are nouns.

Word	Noun	Adjective	Verb	Adverb
basilisk	Yes	No	No	No
mythical creature	Yes	No	No	No

As nouns, mythical creature is a hypernym of basilisk; that is, mythical creature is a word with a broader meaning than basilisk:

basilisk: (classical mythology) a serpent (or lizard or dragon) able to kill with its breath or glance
mythical creature: a monster renowned in folklore and myth

Other hypernyms of basilisk include mythical monster.

basilisk (noun)	mythical creature (noun)
small crested arboreal lizard able to run on its hind legs; of tropical America	a monster renowned in folklore and myth
ancient brass cannon
(classical mythology) a serpent (or lizard or dragon) able to kill with its breath or glance