arrow crabs?

[JOSH]

well with my mantis im hoping this guy stays alive, a have a damsel living with him and so far so good, so i'll get another tankmate or a good battle

[Fish]

Of course your damsel is going to have better odds in a smasher tank... a crab though is mantis-food so I don't think it would last even 24hours.
The arrow crab only have small little claws and not much armour, so it wouldn't even be a good battle - just a waste of $15. Save the cash for hermits and snails, something that will actually strengthen the dactyls. The arrow crab would be interesting in a species tank though... big als used to get them pretty regularly. Seen them a Wais too.

- Chad