Is the forbidden that rare? Doesn't everyone have it?

Now, in Dark Hell City, there are hardly any people left, even though some remaining guards have mastered the power of the forbidden and become the Ghost Emperor. 

But since Lord K has taken over the entire Ghost Realm, there might be others who possess the forbidden power. Helpless, Alexander had no choice but to rise into the air and rush towards the outskirts of Dark Hell City.

Outside Dark Hell City, a dozen guards from the city lord's mansion stood in front of the city gate. Not far in front of her was the endless army of the Endless Abyss. More precisely, it was the army of the Third Ghost Realm. 

An endless sea of ghosts stretched for hundreds of miles, enveloping the entire Dark Hell City. Even beyond the horizon, it was a densely packed mass, giving one goosebumps.