It would most likely be an adjective prepositional phrase because it will modify a noun.
adverb phrase
adverb phrase
adverb phrase for a+
A+ adjective phrase
No, it is not. Mountainous is an adjective meaning of, about, or like a mountain. The adverb form, mountainously, has very rare usage.
adverb phrase for a+
Dark can be an adjective or a noun. Darkly is an adverb.
Adverb.Here is an adverb, not an adjective.
its an adverb an adjective is a descriptive word an adverb is a feeling
An adverb describes a verb, an adjective or another adverb.
It can be an adjective OR an adverb. adjective -- You dog is a friendly dog adverb -- She always talks friendly to me
Shyly is an adverb. The adjective form is just shy.