Returning From The Magic World

The consciousness of a Great Magus suddenly returned to his original body on earth, just before he transmigrated into the magic world.
Nothing has changed, it’s still the same earth.
However, when he looked at earth once more as a former great magus, he discovered earth was not as simple as he knew it to be.
Hidden magus, legendary races such as vampires and werewolves, they do exist, ruling the world through the shadows.
Faced with a former great magus, who possessed as many spells as libraries, would the earth that had been ruled by a few people be able to remain calm?