Black Bull

From the Sonic News Network, the Sonic Wiki

The Black Bull (ブラックブル) is a powerful creature in the Black Arms. It resembles a cross between a giant maggot and a dragon. Due to its large blubbery body, its only weak spot is its single green eye. It can breathe fire and produce Black Wings from its mouth. It appears as a boss after you complete the Lethal Highway and/or Death Ruins stages.