long time ago, i wrote a concept for a sonic fanfic, dealt with sonic and co coming to the human world adn meeting a human character (Michael)

the main concept was the Chaos Combine power, the idea that prolonged exposure to chaos emeralds can cause passive mutations (i.e. Sonics speed, tails intellect, knuckles strength), and when triggered by another emerald (reference to the sonic x cartoons, where emeralds glow when near eachother) can cause a combined being,

in the stroy the human character got an overly huge amount of chaos radiation, which enables him to combine with sonic and the gang, enhancing their ablities, .

this is a picture of Michael in sonic mode, has greater speed, and more resistance to damage

other characters/modes include, Tails, Knuckles, Big, Rogue, shadow, amy and "Last" mode,