Here is a killer mysis shrimp pattern that I use locally. I know it is a bit larger than most mysis patterns, but it does the trick where mysis are present:

KG's South Fork Mysis


Hook:DaiRiki 125 size 16
Thread: 8/0 Clear Mono
Bead: 3/32 silver
Abdomen/Tail:Pearl Krystal Flash -
over-wrapped with clear mono tying thread
Thorax: Pearl Ice Dub