Yes, thank you. I did some research on how to trap a Mantis Shrimp. I am going to try one of the home made traps I read about right now. I realize this would probably be more successful if done in the evening but my friend really wants to get that thing out of his tank. Not only is it destructive on multiple levels but gets irritating after a while hearing the clicking all the time.The new information did not particularly help (but appreciated). Pictures are paramount. Second - if fish are dying rapidly, a hospital tank should be prepared - and the fish moved to that. That will also make pictures easier to take. Then a decision can be made about what treatment.
Mantis shrimp can cause multiple injuries (small) - and you will not necessarily see the 'attack'. Another 'plan' would be to set a trap and get rid of (ask your LFS if they want it) - the mantis shrimp.