Just random notes this time I couldn't fit into the big overview, haha.
At some point in a polymorph's lifespan-- when they reach maturity, when they overcharge for the first time, or some other unknown reason-- they gain special markings at certain spots on their body. These markings persist throughout all forms, and are completely unique to that specific poly; normally they glow when the poly is fully charged or using magic, but some polies have enough of a constant charge going for them to stay lit up constantly unless they're completely exhausted or ill.
The markings can appear anywhere on the poly's body and in different numbers; Icarus is pretty much covered in them, Zaffa only has them on her heads, back of hands, and hips, and Katrine has a single marking on the small of her back. The number of markings doesn't seem to affect anything. When inactive, they show up as a slightly darker shade of the fur surrounding them.
If supplied enough energy or allowed to recharge for long enough, a poly can enter a sort of special state where they're... basically full of energy. When miniform they actually light up all over!
Icarus has an odd quirk in that overcharging will cause xir to shift into a form xe can't otherwise access. It's not known if any of the other polymorphs can do that yet.
Polymorphs can't get sick like organics can, mostly due to only occasionally being close to fully organic depending on the shift; even then, it's rare for a poly to come down with something. They can, however, fall prey to coding errors, random glitches, and some sicknesses caused by tainted or incorrectly refined energy. There are also some cases where a damaged core can cause the poly to feel or act sick.
When a poly shifts, they usually tend to keep some features from their baseform. Anything from palette to general markings to defining features like Icarus's antennae carry over; this makes them easier to identify! This isn't always the case, though, as they can choose to shift completely and be pretty much unrecognizable.
Shifting can change their voice, mannerisms, likes and/or dislikes, and pretty much anything. They're also able to slip more fully into a shift, at which point if the shift is a nonsapient creature they'll act more feral while still having vague hints of their own personality; this can be involuntary depending on the shift.
I've mentioned it a few times, but mentioning it again sounds good: Their core markings always carry over no matter what. :> Changing sizes and shape so often also makes it difficult for polies to wear clothes; it sucks, but they've learned to not get too attached to anything lest it busts apart. Or they usually magic it to where it'll fit them no matter what.
In the midst of transforming, the poly's actual nature as a gooey monster thing tends to show through; it can either happen in the blink of an eye, or slowly and dramatically depending on how they feel that day. And they can pretty much shift anything: extra heads or limbs, mythological and fictional creatures, things they've completely made up themselves, etc. The sky's the limit, unless you're Ica and have size restrictions or are Kat and can't willingly shift at all. Them's the breaks.