MTL - Yu-Gi-Oh!: Underworld Boss, Cancerous Creator God - Chapter 7

Cui Heng was transmigrated to another world and the system told him that the new world he was in was a high-grade Xianxia world.

Transform into Divine Dragon and dominate the world!
He is the only Divine Dragon in the sea who founded an underwater Dragon Palace.
With Crawfish Soldiers and Crab Generals as his followers, wild sharks and gigantic octopuses as his subordinates, he is the dragon that rules the city.

- Description from Novelupdates

A million years ago, he had traversed the Nine Heavens and Ten Earths, braving countless mysterious Life Prohibition Zones, in search of a way to resurrect that foolish woman, but inadvertently learned one earth-shattering secret after another. Thereafter, he went through nine cycles of reincarnation, strategizing over the world, casting his net across the heavens, with the Myriad Realms as his board! In this life, he had returned from reincarnation, his Qi engulfing mountains and rivers, “It’s time to close the net...”

It was just one of those ordinary college class sessions when all of a sudden, texts and quest cards started popping up in the air.

While everybody is flustered by the strange situation, all the lights go dark and the lecture room is engulfed in pitch darkness. Panicked, everybody is afraid of reaching out and taking the quest cards, but not the main character, Seong-woo: He instinctively realizes that he has to pick a card to survive, and he chooses to become a necromancer.

Soon after, a tutorial quest appears, and the entire school turns chaotic. Suddenly, goblins pop out everywhere and start slaughtering people. Survivors find it hard to adjust themselves to all the sudden changes, but Seong-woo overpowers one of the goblins by using his necromancy skill and starts to complete the quest given to him.

Seong-woo continues to grow his power and so does a number of his followers. He is surrounded by the forces of death that vow loyalty to him, as well as talented followers and trustful colleagues, but he is challenged by numerous villains in addition to a system that threatens to degenerate all of humanity.

In a world that is facing a change that it has never experienced before, a necromancer destroys everything with his committed forces