Ok. If you want to house a puffer, trigger, eel of any sort regardless of a doomed ribbon eel all with a mantis, I suggest you get started on like a 500 gallon tank and keep all well fed, but in a 30 g tank it wont work and I wouldnt give it a week before something is dead if not all of them. Ribbon eels are virtually hopless unless you get on that is eating or you have a species tank. Also, if you really want to try this demented idea then go get a ribbon eel, i don tthink he will mess with the mantis more like the other way around. I love mantis shrimps but also hate them. Personally i hope your trigger grows some balls and destroys him.