I use mallard too. The only variation is that I split the tail (stonefly style) and don't include a wing when I tie the pattern. I simply use mallard for legs/gills on each side of the fly.
Rather than tie in a wing, I dub with hare-tron and pick it out the entire body. I like the way it sparkles and traps bubbles underwater. Then if there's a caddis hatch you can clip off the tail and you have a pretty good looking pupae. I suppose this generic pattern could imitate just about anything a trout eats.
This conversation as got me thinking about digging the studs out and hitting the deerfield tomorrow