The lionfish will inevitably eat the gobies and mandarin. If you want to have the larger more carnivorous fish, you'll have to stay away from the little guys. If you wanted to scratch the lionfish off your list, then the eel with others MAY work. It will depend on the size and personality of the eel. Some people keep snowflakes with crabs, small fish, and other inverts and they never touch anything as long as they are well fed. Others have had them make a salt water buffet out of their tankmates, it's really hit or miss.