Oscar pointed at the corpse of the Mirror Image Beast. "Big brother, you better hurry and extract the soul bone. I'll collect some of their blood."
As he spoke, Oscar took out several different styles of containers from his soul tool that he carried around. Before he had his sixth soul skill, he didn't know whether he would be successful or not and naturally wouldn't have been prepared. But being in such a dangerous state all the time, he naturally carried a lot of various items with him, and freeing up some to hold blood was possible.
After all, no Soul Master would easily give him their blood, and his sixth soul skill required fresh blood as a catalyst. Oscar had already thought it through -- he would make a batch of Mirror Image Sausages with the blood of Soul Masters who were not much different from his own strength and carry them on him. That would be enough for self-defense.