Wulfgar's Heroic Sacrifice during the attempt to save Drizzt, a yocohol (Handmaiden of Lloth) has appeared and injured him badly, so to make sure Catti-Bree lives since she's there, Wulfgar begins to sing a song to Tempus and brings the ceiling down on himself and the yocohol, inspiring a Roaring Rampage of Revenge from Bruenor and Catti-Bree on the Drow.
Matron Baerne's sheer and utter annihilation of the Third House thanks to an avatar of Lloth appearing and giving her the power to utterly wipe out the Third House thanks to the deal made with Errtu.
Lloth visiting Baerne to begin with. She pretty much lets herself in, is guided to Baerne and pretty much slaps her verbally and calls her an idiot and then tells her "My powers are returning and together you and I will destroy the Third House with the power I give you.".
Drizzt, Catti-Bree, Bruenor and Wulfgar versus Errtu, one of the most powerful demons to exist. Errtu didn't stand a chance.