sounds like Russian Roulette...I keep a fish in my 6" peacocks tank, but its a nice clownfish that doesnt try to eat the mantis...thus there are few problems... Lion probably be okay, but no sure about those nosey inquisitive puffers (what species?) , I have heard of Boxfish killing off whole tanks so that that could be bad...
But I have heard of crazier things like a mantis and an octopus living together!...so who knows.. I would test the mentality of your mantis to see how aggressive he or she is to fish (I used a little damsel and there was no aggression, then tried the clown and they have been living together happily for over a year)