"Mother of Sorrows" is an orchestral piece from the Season 6 soundtrack.
She falls to the ground and sees the Man in Black. She thanks him for killing her, then dies. When Jacob arrives, he tackles his brother, drags him towards the Heart against his protests, and throws him into the cave. Soon after, the ground rumbles and black smoke pours forth.
The piece begins with an introduction that does not play in the episode. The first movement contains the Light theme and a different variation of the Man in Black's theme from what the episode plays. The second movement begins with the monster's second motif, which quickly moves into the Others' main motif. It ends with Jacob's theme.