Is this appositive adjective a misplaced modifier? E.g. He lived on the edge of a mountain, ancient and forgotten

Solution 1:

Ancient and forgotten are not misplaced and neither would ancient and ruinous be in the second example.

These are called predicative adjuncts, and may occur as modifiers in clause structure or as supplement. Supplements are not restricted as to their position whereas modifiers are more like complements, especially in cases where they occur frequently with a particular verb (CaGEL p263):

He died young.

? Young, he died.

He was born rich.

? Rich, he was born.

Here, the predicative adjuncts young and rich would seem out of place if moved to initial position. However, supplements have no such restrictions:

Angry at this deception, Kim stormed out of the room.

Kim stormed out of the room, angry at this deception

Your two examples are supplements and hence their position is not restricted.

Ancient and forgotten, he lived on the edge of a mountain.

He, ancient and forgotten, lived on the edge of a mountain.

He lived on the edge of a mountain, ancient and forgotten.