no, I don't think that's a good idea. yea the cons may be able to "take care of themselfs" against the puffers, but that is actually a moot point. your fish would probably constantly be stressed. add to that the fact that figure 8's do best in light brackish at least, where as cons should be kept in freshwater. also, if the cons mate, they will claim 90% of the tank leaving the puffers to either become for aggressive or keeping them stuck in a corner.