Future Generations/YMMV


 * Complete Monster: A few characters count as this, though Callous and Johnny are the most prominent.
 * Moral Event Horizon: Even as a villain, Metal Sonic was particularily cruel.
 * Nightmare Fuel: The very concept of Corruption; a supernatural force which can infect and destroy anything from within, including those who use it for combat purposes. Controlling it basically requires you to hone it beyond a normal lifetime, which in essence means shedding yourself of your humanity.