I would highley recommend puffers as they are very interesting fish, with a 55 gallon you could get a toby puffer in there that should be fine. I would say that a puffer, dwarf lion and a snowflake should be fine as long as the puffer isn't too small compared to the other fish. the only thing you may need to be wary of is the puffer nipping at the lions fins however as long as the tank is fed regulary this should be a problem. The only other issue I would see is that I would highly recommend good flitration on this fish as they all produce a fair amount of waste to my understanding so a sump may be of use!