It was just a copy of his attacks, repeating the deafening noises they caused. But it was enough to attract most of the monsters in the area towards the stairs region. And then different types of noises appeared as these masters started attacking as well, the type that came from real fighting.
William was far away from the stairs area when all this happened. He didn't want to be there when dark gold masters were leading such an attack against monsters.
He got lots of ruined buildings standing between him and these bloody battles. But just when half an hour passed and the noises didn't approach him, he knew his trap worked.
The monsters might be weak, but there was no end to them. Not all the masters had the same crazy mind of spending elixirs to replenish their lost spirit power. So it was expected that after one hour, the noises of fight vanished while he saw shadows climbing back towards the plateau area.