pretty much,, Felix has this thing called the "Rampage Virus".
it is not contagious and is EXTREMELY rare. you can not catch this virus, you must be born with it. Felix was the unlucky case of ACTUALLY being born with it. Said virus has MANY consequences and side effects. It can activate "rage mode" or "rampage mode" , a mental state in which everyone and everything around you has become the enemy and you feel the absolute NEED or DESIRE to destroy all of it. Control of your body will no longer be your own and you will act on this impulse to destroy and kill. There is no cure. Felix, however, is lucky. Usually, rage mode will over-load your heart, beating so fast, you die of a heart attack. Most holders of this disease die at the age of 3. Another side effect, however, is a physical change. It only activates when in rage mode, when angry, or when you sense a threat. The skin of the diseased will turn a dark grey, and their eyes a deep red. they will also grow very sharp teeth.