When Sark came in Knuckles and his friends' dimension, he not only killed and possessed the Sonic in that dimension, but managed to demonize most of the inhabitants living there, including Tails, Knuckles himself, Dr. Eggman, Sally, Cream, and Amy. Sark then began to use them as his servants. Eventually, Knuckles decided to rebel against Sark along with Tails, he’s rebellious and demonic