Serpent Sarcophagus

The day I was born, my family was moving the ancestral graves. My father killed a large snake in the coffin that was about to molt into a dragon, and was almost bitten to death by the snake. When I was born, all the snakes swarmed together, and the snakes hissed, saying I was unlucky. A rice woman in the village saved my father with her life and left me a piece of black snake-shaped jade, and was also bitten to death by a snake. My eighteenth birthday just passed, the corpse of the snake from that day reappeared in my family's ancestral coffin ... only the black snake in the jade, desperately trying to protect me, told me the secret of the snake coffin.