What is the subject compliment of sentence room terribly messy?

The sentence "Room terribly messy" is missing a subject and a verb. To make it a complete sentence, we need to add those parts:

The room is terribly messy.

Now, we can identify the subject complement.

* Subject: The room

* Verb: is

* Subject Complement: terribly messy

In this case, "terribly messy" is the subject complement because it describes the subject ("the room").