With the special properties of the Power of Destruction and the Immortality Aura it became increasingly difficult for the Demon of the Ancient Battlefield to heal.
Ancient True Gods possessed great endurance and high regeneration. Some were even said to be able to regrow limbs with the power of their will and their innate regeneration.
This was different from Dilan's Origin ability because it was something that all Ancient True Gods were capable of when reaching a certain level.
However, it was exactly this great regeneration that didn't work for the Demon of the Ancient Battlefield, not while facing Dilan!
The Power of Destructio and the remnants of the Immortality aura circulated through his body. They restricted his cells from healing as fast as they would usually heal him.