"Craggily" Adjective or adverb?

I love the word craggily! I looked it up and found that it is considered an adverb of the word "craggy." However, whenever I've seen this word used or spoken, it's always used as an adjective. i.e. "Look at the beautiful, craggily mountain." Another adverb used as an adjective is the word scraggily. Well, I was wondering if this is just improper use, or if there is some obscure grammar rule that justifies us using adverbs as adjectives.