Eris's two-part floor-wide ritual that makes everyone invulnerable, then freezes and abducts nearly every combatant.
With no warning, a yellow radiance settled over Carl, his army and the entire Madness force at once, accompanied by the message that all were invulnerable until the completion of the Chaos Ritual. Rosetta recognized it instantly and told everyone to hold on. Part one was Bear Witness, which froze every unsheltered creature on the floor; part two was a level-20 Bring Forth the Witnesses, which launched them all into the sky and away.
The ritual ended the battle for The Madness Castle before the first charge, stranded the survivors with no long-range teleportation for an hour, and scattered team rosters so badly that Rosetta warned everyone they would wake up mixed together and should run for their own people.
The chapter's turning point, wiping both armies off the board and forcing every commander to improvise.