Could be Lymphocyistis. It is a virus, no known cure. Was your puffer and your molly in the same tank, did you ever use the same net between the tanks, move something between tanks? I have a Thorichthys Aureus Blue ( S/A Cichlid ) that has it. I thought it was fungus and tried two different treatments for two weeks to no avail. Then I called the person I bought him from and he told me it was the virus. His advice was to net the fish and pull as much of the growth off as i could, wait one week and remove any remaining growth and keep this up until no more growth is present. I just removed the growth a second time and he looks good for now, I will keep him in the isolation tank untill I dont see any more growth for two weeks. I did a search on the net and there is a lot of info, including pictures. Take a look and see if that is what it is. Good luck Keith