he's an Anti-Hero, thought that would be pretty obvious after the true ending to shadow the hedgehog and the fact he plans to keep his promise with Maria...
Shadow was created as the ultimate lifeform to have the same abilities and same speed of sonic, alike metal sonic, sonic's robot doppelanger. Sure shadow has done some evil deeds and he has a dit before he is evil, but deep down shadow has a cœur, coeur and will try to help those he knows .
Hes and anti-hero so basicly neither and both when u think about it is both but also neither becuz he dosent care for the planet yet he saves it and he hates G.U.N yet he works for them