My favorite and least favorite version of Shadow the Hedgehog is the one from Sonic Boom. In Boom he's a terrible representation of Shadow as a whole character and what he initially represented. But he's a fun character to experiment with because, I can make Shadow's initial backstory 10 times worse.
Like imagine instead of the Space Colony Ark being nice at first and then rated by G.U.N., but now it was always supposed to be a government weapons facility. Maria's still in the picture cuz he needs her but she is the only redeeming aspect about his life.
And one day they deem him too dangerous too much effort to control (maybe he hurt Maria). So they put him in cryostasis. And he's woken up by Dr Eggman, Eggman not knowing how to control or work with Shadow, he just runs off and now he just lives in a cave trying to forget the horrific of Space Colony Ark.
He's angry at living beings for treating him nothing more than an object to experiment on. He's lived through the worst and still has yet to experience the good it has to offer besides those short moments with Maria.