Having come to the decision that he needed to find a way to deal with the Peak Soul Ascension Realm illusory beast that was in control of the current area of the valley he found himself inside of at the moment, Xuan Hao began to try and look for any weakness that he might be able to exploit in the illusory beasts. Using the countless weaker Domain Lord Realm illusory beasts present in the valley to find these weaknesses.
During this process, he also realized that the illusory beasts he had killed over the past month would reappear after a set amount of time had passed. The weaker the illusory beasts were, the faster they would reappear.
Although, during this time, only illusory beasts below the Soul Ascension Realm had appeared again. Maybe this was case he hadn't discovered this happening earlier, as he mostly focused his attention on the Soul Ascension Realm illusory beasts who helped him comprehend the Dao of Illusions.