Harry Potter : Reincarnated as The Greatest Wizard - Chapter 80 - Experiment

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

Zeke Draker,The first failure to awaken among the direct descendants of the Dragonslayer family.Expelled from his family for possessing the talent of a Healer instead of a swordsman.Zeke struggled desperately to become stronger, only to face a miserable death.At the moment of his death, strange letters appeared before his eyes.[The soul of the Elder Dragon is engraved into the spirit of the one who possesses will.][An irrevocable and promised power is activated.]When he regained consciousness, he opened his eyes twenty years in the past, in the family that had abandoned him.“If I can become stronger, I will use anything at my disposal.”A new awakening with an immortal power.The legend of a Dragonslayer with a different class begins.

Black belly, online IQ

Reborn in the magnificent world of cultivating immortals

Everything is based on ‘stability’, and everything is settled before moving, and when moving, there is a thunderbolt, and after moving, there is no sound.

Hidden cards, refining elixir, practicing escape, and practicing spells.

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- Description from novelbuddy