I Become Invincible on Earth After 300 Years of Guarding the Mortal World

Zhang Li transmigrated to the world of cultivation and obtained the cheats of fusing all things.
Fearing that the clan would find out his secret of "reincarnation", he chose the task of guarding the mortal world for three hundred years.
Before leaving, he used his cheats to make a big deal.
He fused ten lower-grade spirit stones to obtain a medium-grade spirit stone.
A medium-grade spirit stone could be traded for eleven lower-grade spirit stones.
Fuse ten medium-grade spirit stones to get one upper-grade spirit stone.
An upper-grade spirit stone could directly trade one hundred and thirty lower-grade spirit stones.
Fuse ten upper-grade spirit stones to obtain one spirit crystal.
A spirit crystal could be traded for one thousand five hundred lower-grade spirit stones.
...
Other people said that the task of guarding the mortal world was to give up cultivation. No one could rejoin the world of cultivation from the mortal world after three hundred years.
Zhang Li, who went to the mortal world with a storage bag full of spirit stones and various cultivation resources, did not buy it.
"Fellow Daoists, see you in three hundred years."