Defeating a Peak Beyond Limit Stage Archdevil
Originally Zatiel did not intend to fight alongside the Imperial Depravitas during his mission in Abyss or Baator. Still, due to the paranoiac nature of Archdevils, things went a little out of hand.
The Archdevil that dominated this city had the name of Horun and was supposed to be a weak Beyond Limit Stage existence.
However, not only had Horun hidden his true power for thousands of years, which was at the Middle Beyond Limit Stage, but he also took a powerful drug that pushed him to the peak of the stage as he saw the might of the Corrupting Mist and Zatiel.
If the Neo-Demon had taken a few years to research this Archdevil personally, he would have noticed Horun's true power and hidden tricks. But none of that mattered anymore.
Zatiel did not waste even a second thinking about what could have been done differently and instead summoned the Imperial Depravitas to his side.