Never used a mouse fly for targeting trout but I had a 46 inch Northern Pike hammer one last fall. It's one of my fav patterns for Pike. Catching Pike on a fly rod is an absolute blast and you don't need to worry about a dainty presentation. In fact, the bigger the splash the better. A mouse fly with a "toothy critters" leader on a #9 or #10 rod/line set up in pike water is heaven to me. Second best to the mouse would be a baby duck pattern.
