Xiao Lin touched the spatial ring on his finger. Although the professor told him that when he reached a proficient level and that he would not need to use death aura to transform elements, he was still a beginner and he needed to rely on death aura to perform element compression. He felt that it was a little too rushed.
Extracting death energy from the spatial ring was the quickest thing that came to mind. After all, he could not summon the black knight anywhere or anytime wanted. Fortunately, this ring was completely controlled by his mental strength, so it was possible to properly extract the black knight's breath of death.