As the Beast was a Variant and a Rare Elite, Luke suddenly got the idea to use the 'Sound of All' skill on the Beast, and if his last hypothesis that he came to would be proven true then it meant that he acquired a Unique Grade skill that is no less than a Mythical Grade. 'Sound of All' called Luke as he dived into the World of Darkness to find about the Beast in front of him. Luke heard fewer murmurs of spirits within the cave than outside, but he didn't let that distract him from his focus on the Beast.
In the world of darkness, his focus was on the image of a green bead that came into his mind. If Luke had to say something about that skill is that he technically can't see anything with his eye. In front of his eyes was just full black, a complete world of darkness where he could see nothing but in this world, his only source of perception was his ears. His visuals were gone but he could still see images through sound which sounded absurd but to Luke that was the truth.
