Meet Violet, the sister of both Puff and Crimson.
Violet is the glutton of the trio, always loving to eat (when she feels like it) and always getting fat (again when she feels like it). Similar to how candy makes Quartzie an inch fatter per piece, Violet gets a quarter of an inch fatter with every piece of FOOD she eats. So, for example, a big meal will easily make her go from thin to morbidly obese in seconds! As I said twice before, she only chooses to eat a lot when she feels like it, so she'll not always be fat when you see her.
As some of you may notice, these three Sylveons all have something in common, Crimson is based around diapers, Puff around inflation, and Violet around fattening; all three of those are my favorite fetishes!