MTL - Wuxia: The Identity of My Dragon Head Has Been Exposed - Chapter 111

When I woke up after a pretty crappy death, what greeted me was one of those famous fantasy worlds! I didn’t expect anything like becoming the strongest with a common job, or rising to the top with the weakest class…All I wanted was to live a slow farming life, but the world just wouldn’t leave me alone! And so I equally backstabbed good people and bad people alike, becoming a villain with a true sense of equality and just when I was about to retire and enjoy a proper life on a farm…“Master!”My former disciple at the evil organisation, currently the hero of justice came looking for me. Can’t you all just leave me alone?

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

For the wine to be drunk on her wedding night to actually have been a cup of poison and for the one to poison her to be her husband, who would believe it?