After a couple of years trying different techniques and materials - like super hair, ultra hair, bucktail, fish hair, slinky fiber, big fly fiber, fox tail, super fiber, EP fiber, vegetable fiber (agave fibers), etc. - I achieved to tie a good fly as a wanted with a huge shape underwater, made with horse tail hair, which sinks fast but it is still light and breathable.
I'm using this fly to catch big Golden Dorados, and it's working pretty well! I'm thinking of calling it "Big Horse".
This fly is derived from another streamer tied with bucktail (Mix 60º). I used jig hooks 60º (Henry Cowen - "The Jig is up") and dumbell eyes as a Clouser Minnows (Bob Clouser).
The tail was made with feathers tied in "V" like a Cockroach (Tarpon Fly).
The body also was inpired by Lefty Deceivers (Lefty Kreh) and Hollow Fleyes (Bop Popovics).
The head is tied with horse mane. The tinny fiber is better to make a conical head inspired by Whistlers (Dan Blaton) and Andino Deceivers (Carlos Ingrassia).
I doesn't use flash fibers. The fly is simple and very tough, easy to cast with a #9 fly rod and 300 - 350 grains sinking tip fly line.