mortal vs deathly

mortal is a noun but deathly is not a noun.

Word	Noun	Adjective	Verb	Adverb
mortal	Yes	Yes	No	No
deathly	No	Yes	No	Yes

As adjectives, mortal and deathly are synonyms defined as:

Other synonyms of mortal include deadly.

mortal (noun)	deathly (noun)
a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

mortal (adjective)	deathly (adjective)
subject to death	having the physical appearance of death
unrelenting and deadly	causing or capable of causing death
involving loss of divine grace or spiritual death
causing or capable of causing death

mortal (adverb)	deathly (adverb)
	to a degree resembling death
	to an extreme degree