The Perdigon ("little pearl" in Spanish) came out of the Spanish competition scene in the 2000s. The design priority is sink rate: a big tungsten bead, a body made of thread or quill, and a hard UV-resin or nail-polish coating that smooths the surface so the fly cuts water like a stone.
Most Perdigons are sized 14-18 with 3.0-4.0mm beads. The hot-spot color (pink, chartreuse, orange) behind the bead does the attraction work; the body color (olive, black, brown) suggests the bug.
Fish it on the point of a Euro rig when you need to be on the bottom in a deep run. Tie a softer-bodied nymph as the dropper above — the Perdigon gets you down, the dropper does the eating.