Funny question...both of mine are brutal when I introduce prey: Fiddlers, other crabs,ghost shrimp.
However, I have introduced a damselfish with each (Domino with one, yellow damsel with te other).
Both fish are alive, well (Occasionally nervous), and the yellow even hangs out in the burrow with the mantis. The mantis don't even make threat displays unless they are going to molt, then they ward off the fish for a few days to make sure that they won't be messed with during the molt.
These are 4.5 and 5" peacocks respectively, and the tanksare smaller , 12 gallon Eclipse (Moving them to their own 30's soon folks, never fear). I do feed regulary, however, and it might be a different story if I went a week without offering food.
My ternatensis is my most aggressive, with one of my chiraga and my viridis both close behind.
Hope that helps.
-Ron