Thoughts on quilling (when hedgehogs, porcupines, echidnas, etc. shed and regrow their quills) in the Sonic-verse?
I assume you mean quilling as shedding all their quills, not losing a handful here and there, like we'd do hair? I think the latter isn't really noteworthy, maybe aside of the fact that it leads to the occasional quill being stuck in couches or blankets, which has the potential to be annoying for the hedgehog's roommates and friends. Tails probably knows to check before sitting on something Sonic lounged on, because he accidentally sat on a spike often enough.
They'd probably also lose quills when they injure them (all that spin dashing and smashing into metal objects spines first they do seems likely to result in broken off or bend quills). Injured quills would logically need some time to regrow. Real hedgehogs can also lose quills when gravely ill or very stressed. We see the characters in enough of stressful situations to maybe assume they don't get bald spots as soon as they're stressed out, but maybe if it's really bad?
Actual quilling (shedding and regrowing all their spines) is something only baby/young hedgehogs do, to my knowledge? And they do it only once, when they lose their softer and usually lighter coloured baby quills and grow their adult spines. I'd imagine that to be an uncomfortable affair, it probably itches or stings and is overall a right nuisance.
Mobians seem to mature at a rate more like humans, so if we extrapolate from real hedgehogs, this growing adult spines thing would probably be something to happen in their early teens/at the beginning of puberty. It's my personal headcanon for why Classic Sonic is lighter in colour and has shorter spines than Modern Sonic. I go with them being the same Sonic, just at different age (they time travel rather than are from different universes). Modern Sonic is 15/16, depending on game. Classic Sonic is 10-12 in my head. So Classic Sonic is more of a kid hedgehog yet. He's smaller, he has shorter arms and legs, and shorter and lighter coloured quills. Come Sonic Adventure, Sonic is a little older, a teenager. He grew his longer, darker blue adult quills at some point before that game. I think they'll be tougher, too, making him less likely to injure them when shredding robots with them.
Echidnas work different than hedgehogs here. Echidnas hatch from eggs, and when they do they're tiny, more embryos than babies. They then stay in their mother's pouch for a while, until they start growing spines (and thus get too spiky to keep in a pouch; the poor mother echidnas would get poked all the time). I don't know if echidnas even go through a complete quilling after that again. I can't find anything about that happening, so maybe they're already equipped with "proper" spines by the time they leave the pouch. *shrug* Maybe someone who has actually seen a real life echidna/knows more about them wants to throw in their two cents?
Until different information comes around, I'll just assume echidnas have a full set of spines from an earlier age (like, one or two years or so) on, hence why Knuckles never changed colour.
I also don't know if porcupines quill like hedgehogs do, but they shed individual spines as part of their defence when attacked. They point their spikes at the predator out to get them and spines are shaken loose and might end up impaling whatever attacked the porcupine. The lost spines then grow back. Maybe a Mobian porcupine character would end up leaving robots behind with quills stuck in vital parts?
