mellow vs mellowly

mellow is an adjective but mellowly is not an adjective.

Word	Noun	Adjective	Verb	Adverb
mellow	No	Yes	Yes	Yes
mellowly	No	No	No	Yes

As adverbs, mellow and mellowly are synonyms defined as:

mellow (adjective)	mellowly (adjective)
slightly and pleasantly intoxicated from alcohol or a drug (especially marijuana)
unhurried and relaxed
having a full and pleasing flavor through proper aging
softened through age or experience

mellow (verb)	mellowly (verb)
make or grow (more) mellow
soften, make mellow
become more relaxed, easygoing, or genial

mellow (adverb)	mellowly (adverb)
in a mellow manner	in a mellow manner