Build
Three bands, what a heavy Jeli is worse at, and how it comes off.
A Jeli that is fed more than it needs puts on weight. There are three bands: Fine, Heavy and Round. As with Mood, you're shown the band and never a number.
Weight starts to apply from the juvenile stage. Hatchlings don't gain it.
What it costs#
A heavier Jeli is slower and doesn't jump as high, which you'll notice in Run before you notice it anywhere else. Walks do less for its mood.
Nothing about it is hidden or sudden. A heavy Jeli always still agrees to play; it's just visibly worse at it.
Taking it off#
Walking, running and time. The same exercise that pays hearts takes weight off, so there's nothing extra to do and nothing to buy.
What it never does#
Weight never kills a Jeli and never makes one ill. Overfeeding in one sitting has its own short, obvious cost at the time; weight is the part that lasts beyond that afternoon.