Mount the hook and lay a thread base back almost to the bend. Thread weight matters here: use a 6/0 or 8/0, or a Semperfli 12/0 waxed which is strong enough despite the number, because a dubbing loop is coming.
Slide a 3/32 in tungsten bead onto a #17 embroidery pin and trim the pin with wire snips so nothing pointed sticks out the back. For this hook and bead the balance point is about two bead widths forward of the eye; if you are unsure, tie one and float it in a bowl of water before committing to a batch.
Tie the pin in with three or four wraps and check the position, then superglue each side and add another layer of wraps. That glue layer is why Svend's beads do not shift when the fly hits a rock.
Trim the tip out of a Fish Hunter marabou feather. It tapers better when wet without it, and stroke the fibres back. Find where the bulk of the feather ends, ignoring the long wispy tips, and measure that point to one overall fly length.
Tie in with three or four loose wraps and check the length. The wispy tips beyond the bulk are what give the taper, so leave them.
Bind the marabou forward all the way to a wrap or two behind the tungsten bead before trimming. Running it up the shank means the later glue forms a cone around the shank and the pin. The second reason these are durable.
Fold a strand of gold Krystal Flash in half, tie it in on the near side with two or three wraps, then bring it up and over and pinch so the flash lies down each flank.
Form a five or six inch dubbing loop, wrap back over the shank, and twist so the X of the loop sits right at the back of the fly. No gap to fill later. Colour the loop thread orange with a marker rather than changing thread.
Pull a pinch of Zero Gravity Dubbing about half the width of a pencil, stack the fibres, lay them into the loop, then spread them out to break up the clumps. Twist gently. Pull too hard and you snap the loop.
Superglue the shank again immediately before wrapping the loop, so the body goes down into wet glue. Stroke the fibres back as you wrap so you do not bury them in it.
Wrap the loop in evenly spaced open turns, not touching wraps. This dubbing gets bulky fast, and a sparser leech fishes better. Tie off, pinch the material back, and leave about a bead's length of clear space behind the bead.
Superglue the thread wraps, then dub a sparse long noodle of shrimp-orange Ice Dub and build a collar, jumping back behind and wrapping forward over your own wraps.
Finish with the thread in front of the collar and take one full wrap to sweep it backwards. Colour the thread red with a marker, build the head, whip finish, and brush the body fibres out.