Maroon clown fish are mean! I was looking for a box that said "the clown will hurt the mantis". I am guessing if it is a large clown, then the mantis will not come out very often. And if its a smaller clown then it might get killed. In my opinion it is going to be very hard to pull off. If you are looking to add a fish or two, I would suggest a damsel. As you might already know they are cheap and fast. worst case scenario with the damsel is it becomes a lunch that cost a few bucks.