They are similar to lions, but they are ambush predators. They have a very big mouth so they are not safe with smaller fish or inverts. So far anything that floats by him he has eaten, krill, shrimp and squid. Their seems to be alot of people that have problems converting them to frozen, but this guy if it fits in his mouth he eats it. He dug a cave behind and underneath one of large pieces of live rock. He hangs out there unless hungry then you see him like in the pics. He is extremely territorial of his cave and rock, he will display with mouth open. If that don't work he will lunge at the tresspasser with mouth open. They wasp has learned to avoid that spot. They are also most active at night.
They will not mess with corals, but I think your smaller crabs and such would get lunched. They are venomous, so you have to becarefull when digging around in the tank. You don't see him much, but itis fun to look over the tank to make sure one of those rocks is not hungry
HTH
Brian