Drawing by Laurel Wilson; inspired by Wayne Barlowe's version of a Golem in his book Barlowe's Guide to Fantasy. This picture was modified from that one.

Darla is a Golem, and is Dagger Dophim 's Mirror Guardian. He simply serves as her Guide when she's in Mirror World. Golems are men made of clay. When Dagger comes into the World, she must "activate" Darla by carving the word "ALIVE" in his forehead, then shining the light reflected off her talisman on the word. When she leaves, it is a good idea to carve the word "SLEEP" in his forehead to allow Darla some time to rest. (Guardians need rest too. :D)
All of these types of Guardians are not allowed to mess with the fate of the mortals they guide; they cannot do anything protective without being told, and can only give advice, not force the mortal to do what they think is best. They are also not allowed to lie.
Darla is 7 feet tall. Dagger feels very close to him.