He thought the worlds the other 4 had created still lacked something. Though the plants Frea had created were interesting they were not lively enough to keep him entertained. Zrook could not think of what was missing but he knew something was, in search of his answer he traveled to the furthest depths of the universe, beyond the creations of Ar’tress and the others. It was there he found The Darkness it was trapped The Phoenix had not given all it’s power to The 5, it had changed some of it’s power into a cage. A cage to hold The Darkness.
The Darkness convinced Zrook to break the cage and told him what was missing was Darkness, it corrupted Zrook and eventually convinced Zrook to let it into his consciousness. Zrook was charmed by The Darkness and oblidged. The Darkness corrupted Zrook.
Zrook retunred to where the other devines where created the planets and under The Darkness's guidence created monsters to destroy the worlds the other devines worked on. The other devines could not destroy these creatures as they where forbidden to destroy or kill by The Phoenix on creation. So, they created there own sentient beings.