The Copperhead Crabbit is my go-to tailing redfish fly. It imitates the fiddler crabs that redfish feed on when they tail on flooded spartina flats during spring tides each summer. It has all of the elements I look for in a crab fly; decent weight, castability, splayed claws, and movement even when the fly is resting on the bottom. The gold mylar makes for great visibility, even in thick grass or dirty water.
This pattern is constructed from gold mylar tubbing, bunny strip, wide hackle, and lead eyes. I prefer a heavy wire hook and large lead eyes to get the fly down fast. You can use a lighter wire hook and bead chain eyes in shallower water. I prefer a single mono post weed guard for flooded spartina grass.