Apart from the Blessing Bestowment, the fiends were also given the Akass Formation to use in case of emergencies.
The Akass Formation was one of Eren's trump cards that he had used against Carvel and his powerful demon pet—a wyvern named Akass. He had named the formation after the wyvern when he slayed it with the Formation's help.
After creating one of his pseudo-avatars with the Profession of the Runemaster, Eren asked the pseudo-avatar to craft many sets of artifact rings required to deploy the Akass Formation.
This Formation showcased Eren's personal touch to the traditional Battle Formations used in the world of Anfang. Nobody even in Labh Salem would believe that such a formation was conceptualized and created by a single entity.