Chaos Mode, known before as Amok Mode.

The Character becomes more Chaotic and can make an unexpected moves,
even than in Evil Mode.

Parts of the Character's body may take on an unnatural shape.
In case of Clone Sonic "Tune-Up!" :
~ spikes are not only raised up, they can also wave,
~ longer fingers,
~ each claws extend at a different distance,
And facial expression:
~ making like .EXE creepy smile,
~ sharper and longer teeth,
~ even more blood flowing from the eyes.

And it's all made to make the player feel even more anxious.
Also, the Character become more thirsty and hunger for F.E.A.R! and can more likely bite the player, in this case Silent "Player-On!" / "Avatar-On!"