In Tide Town, inflation/expansion/weight gain is a rather uncommon thing for anyone to do, but that doesn’t mean that there isn’t a sizable group who enjoys it, (i.e. all of my current OCs). For how natural it is, it isn’t very natural since all of Tide Town and it’s peoples are founded/made from one strain of magic. Even though everyone is tied to magic in some way, the methods used to inflate someone are generic, with magic being rarely used at all. And while it is technically possible to inflate anyone, depending on what attributes that individual was granted, they can only get to a certain size before bursting. Cephalopods, Marine Mammals (including mammalian sharks), plant based entities, and pufferfish are known to be ideal for large sizes.