Just as Midnight felt the undead were going to enter the room she had made her way in to, she felt a shake that made every ruin appear to be in torment. The unique darkness mana that was flowing around was only from one place. One being. Specifically, one royal dragon in anguish. Mordant.
As Onyx and Midnight had felt this, so had the undead. Those that were moving through the ruins as they were guided by the unseen forces of the controlling undead began to follow the source to attack. Likewise, Midnight and Onyx used that distraction to weave through smaller passageways, cracks, broken walls, and many odd rooms. They ignored the things on walls and the ghastly sights within the rooms.
Every bit of their effort brought them further from the slower undead. The undead were slower due to their weaker state. The daytime was still able to affect them to some degree since the light elemental mana was in the air. It might not touch them, but natural weakness was still weakness.