i would stay away from the eel for sure, if the eel is too big it will eat the mantis or if the eel is too small the mantis will probably kill it, especially a ribbon eel. mantis' dont like other things in their caves. on the other hand a relatively small lion should be ok. ( i'm the one with the fuzzy dwarf and smithii). frogsifh might def try to eat a mantis. my lion seems to like my mantis though...they sit right next to eachother and watch me at my computer. the lion doesnt seem to recognize the mantis as food, granted its almost as big as he is. I was surprised that the mantis doesnt attack the lion even when he sits at the entrence of the mantis cave.