Eurogamer just put out an interview with Kazuyuki Hoshino, who's designed multiple Sonic characters, on the process for designing Shadow and other Shadow-adjacent stuff. It's a great read, definitely recommend taking a look. Four most interesting points: Shadow's original full name was "Terios the Prisoner" If you've ever wondered why the Terios designs are so hilariously edgy, Shadow was going to be a full-blown villain before evolving into an antihero. This was the impetus for shifting away from the Terios designs and more towards what we ended up getting. The two biggest inspirations for Shadow's design were (A) Metal Sonic, who Hoshino also designed, and (B) speed skaters. Metal Sonic's jet engine and the basic idea of rivaling Sonic's speed in a unique manner influenced how Hoshino designed Shadow, and he settled on having Shadow skate If you've ever noticed that Black Doom resembles Wizeman from Nights into Dreams, that's not a coincidence, as both were designed by Hoshino. His red-and-black coloration was to create a visual link to Shadow, since they're related genetically. Link to the interview here. Also has some cool concept art, most of which I believe was first revealed as unlockables in Shadow Generations.
I remember hearing that Terios was going to be a tenrec instead of a hedgehog. I wonder if that was something Sega was actually considering or just a fake rumor
Funny to think about how these things work out and, while this problem seems obvious, that the best outcome oftentimes might be reached very organically, as it was here. It's easy to take for granted, but Terios' design really doesn't gel well with the rest of the cast while Shadow does that much better through better adhering to the established design conventions in addition to keep things simple and symmetrical.
Added all this to Shadow's wiki page alongside stuff Iizuka revealed in the Anime Expo interview - God knows how much undocumented development information has already been lost to this forum due to people not doing this as soon as possible.
Terios looking even more like Sonic than Shadow does, as well as the "Prisoner" surname, make me wonder what his backstory was gonna be. Maybe a failed Sonic clone developed by military, a kind of experiment gone wrong?
I never even thought of the connection between Black Doom and Wizeman but that is such a nice little connection
