When I read the novel Breakfast at Tiffany's, I came across the sentence as below.
Then he was standing in front of her, hangdog and shy.
I could hear Doc Golightly’s footsteps climbing the stairs. His head appeared above the banisters, and Holly backed away from him, not as though she were frightened, but as though she were retreating into a shell of disappointment. Then he was standing in front of her, hangdog and shy. “Gosh, Lulamae,” he began, and hesitated, for Holly was gazing at him vacantly, as though she couldn’t place him. “Gee, honey,” he said, “don’t they feed you up here? You’re so skinny. Like when I first saw you. All wild around the eye.”
I'm not sure whether the phrase 'hangdog and shy' is adverbial or subject complement. To me, it seems that the phrase modify subject "He" and also it's a adjective phrase, so in some ways I think its the subject complement. But according to the explanation on Grammar-Monster, It seems that it is not a subject complement at all. Grammar-Monster explanation is as below.
A subject complement is a word or phrase which follows a linking verb (e.g., to be, to become, to appear, to feel, to look, to smell, to taste) and describes or identifies the subject. A subject complement is either an adjective, a noun, or a pronoun. For example (subject complements shaded): He will be fine. (The linking verb is will be (i.e., the verb to be). The subject complement describes the subject He. It is an adjective.) Ben is a policeman. (The linking verb is is (i.e., the verb to be). The subject complement identifies the subject Ben. It is a noun.) I am he. (The linking verb is am (i.e., the verb to be). The subject complement identifies the subject I. It is a pronoun.) That pie looks burnt to a cinder. (The linking verb is looks. The subject complement describes the subject That pie. It is an adjective. Don't forget adjectives (just like nouns) also come in the form of phrases.)
And I was totally confused by this sentence.
Capote, Truman. Breakfast at Tiffany's (Vintage International) (pp. 71-72). Knopf Doubleday Publishing Group. Kindle Edition.