Mantis shrimp will eat anything even remotely close to being alive.
While I was working for a collector in Miami, we dove and collected for local schools, zoos, and large private tanks...we came across a couple customers asking for mantis shrimps (1988-89). So while collecting mated pairs of coral banded boxers I found 2 fairly large mantis. Both were 5-6" and brillantly colored much like an motor oil sheen on water (chromatic blues, greens,etc.).
To make a long story short...while I had instructed the new kid on how not to handle the mantis, called thumb splitters in the Carribean, I had somehow forgotten to tell him to not allow them to be removed from their isolator keepers. So he let them both go in the same tank...I was called in from another job to get them out as the kid was on his way to the hospital with 3 deep cuts in his palm...he picked one up like a hotdog
When I got there, the hunt had been going on for 20mins already. The pair of them creeping about, just looking over the top of the LR to catch sight of the other, and then scooting at 600MPH to the other side of tank to catch the other mantis unaware...it was a ballet that ended like and opera...the fat lady certainly sang that day. Both died from deep wounds.
While these guys are on my most favorite list, along with Taco..I mean octopus, sargasso anglers, and cuttlefish...they must not be allowed to be introduced into a community tank, unless you want to clear the tank of all moving creatures.
The two basic types of mantis are clubbers and blades. The clubbers use a bash and grab style of kung fu, where as the bladed ones have nasty shapy rigdes along their forearm that they use for the snap and cut kung fu.
I had a small clubber mantis 1" chase after a huge mottled pistol shimp 6" for a day at least. The mantis gave up, but I think the fear of god was put into that pistol shrimp.
Ray