mortal vs merciless

mortal is a noun but merciless is not a noun.

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

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

mortal (adjective)	merciless (adjective)
subject to death	having or showing no mercy
unrelenting and deadly
involving loss of divine grace or spiritual death
causing or capable of causing death