I'm Trapped Inside a Prince as the Most Powerful Entity - Chapter 18: Return

This is the tale of an earthling, who transmigrated as a dying third-rate god but somehow rose through the ranks, gaining followers and eventually causing the Fourth Great Apocalypse.

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

Through an array of coincidences, Alex comes to learn that making pills is one of the best ways to earn money in the game, 'Eternal Cultivation.'

When he returned to the World of Martial Arts, the game was filled with blood and battles! Chen Kaixin had chased after the footsteps of the one emperor, two empresses, three princes, seven dukes, and thirteen aces for three years, but during the eve of the Sword Among Us tournament in Mount Hua, he was ambushed by evil bastards, and was killed so much that his level dropped to that of a newbie. He completely lost the chance to join the ranks of the powerful players in the game! In great disappointment, Kaixin quit the game and got drunk so that he could forget his sadness, but during that stormy night, Chen Kaixin found that he had actually dreamed for a total of three years, because when he woke up again, he woke up to three years ago, when he was still a student.