I Became a Heavenly Master at the Age of Eighteen, and I Used the Forbidden Curse

One day my grandfather told me that after you have enjoyed the honor, you should also bear the corresponding responsibilities. … After Gao Zijing's eighteenth birthday, the gate of hell opened wide, a red night covered the sky, and hundreds of ghosts walked at night; all living beings were devastated and the human race was miserable. The evil ghost couldn't resist the thunder spell that was thrown casually, and angrily said, "Boy, you don't have martial ethics. You just started using forbidden magic." What forbidden technique? This is what I learned from the book.