Good on ya for contributing to the 'Classics' Bigdon.
Is it a lure? A 'wet fly'? A nymph? fry? It's all of those, and more.....
The Cormorant is a wicked wee fly.. most versatile too. It'll catch in most conditions, on most waters, and in any month of the year. It'll do a grand job on any line, anywhere on the cast. Fish a team of three or four, or in conjunction with blobs, lures, nymphs. Slow, fast, you name it. It's a rare day indeed when the Cormaorant fails to tempt a fish or 5.
The movement and pulse of the Marabou is a key trigger, but keep them on the sparse side for maximum 'suggestability'. 'Layering' two or three colours in the wing can also help create and exagerate the illusion of movememnt.
I like to add a wee throat of hen, or sometimes a couple of complete turns, just to add a little extra movement. Seems to balance it up a little for me. Not that a fly with this track record needs any help from me. Just my personal twist.
Here's a couple of examples..
Olive
Hook: Kamasan b175 8,
10,12
Rib: Clear or dark Olive spanflex (clear with this one)
Body: Mix - Olive hare's ear, 'Sun Yellow' rabbit, plain hare's ear.
Wing: Marabou Mix - Olive,Golden Olive, Dark Olive, layered light to dark.
Head Hackle: Dark 'Brown olive' hen.
Cheeks: JC splits dyed chartreuse.
Thread: 'Brown olive' UTC 70

Black & Green
Hook: Kamasan b175 8,
10,12
Rib: Green Holographic.
Body: Black Seals fur.
Wing: Marabou Mix - Black & Damsel olive
Head Hackle: Grizzle hen dyed dark olive.
Cheeks: JC splits dyed chartreuse.
Thread: Black UTC 70.

Hare's Ear
Hook: Kamasan b175 8,10,12
Rib: Red Holographic.
Body: Hare's Ear.
Wing: Marabou - Golden Olive (Castle Feathers)
Head Hackle: Furnace hen.
Cheeks: JC splits.
Thread: 'Brown olive' UTC 70