Well mysis are almost as big as he is - lol
I have a green clown goby that will go after mysis, but IME the yellow ones can be harder to feed. This is a fish that should go crazy for frozen cyclopeeze - do you have local access to this? If none of your LFS's have it, chek with your nearest reef club, someone would know where to get it. I know before we had local suppliers our club would organize a group buy.
They are such cool fish -one of my favorites