Shadow is a hedgehog from the 1950s who has supposedly spent 50 years in cryo-statis. The truth is he was attempting to beat Sleeping Beauty's record for the longest time spent asleep but he was woken by a Goomba which attempted to eat him.
Shadow was having a rave in 2005 when Sonic came along and got the giggles and laughed at him an then he hit Sonic who started crying. Later when Sonic tried to take over the world, Shadow was the only person who dared to try to stop him.
After Shadow got fired, he went back to bed to try and make it to 75 years.
Shadow may have also been fired because of his fierce out-going personality and the fact he flirted with another student, namely a Goomba which was male and fancied Princess Peach.