During the Brood War, the Fleet of the Matriarch arrived on Char to retrieve the Khalis, Praetor Artanis suggested that they damage the second Overmind in order to send it into remission and give the protoss time to retrieve the crystal. Should it have been attacked, the second Overmind would have retreated into its Overmind Cocoon.
Later in the war, the Sarah Kerrigan and Zeratul joined forces to defeat the second Overmind. After Dark Templar forced to work for Kerrigan destroyed the Overmind, a cocoon emerged from it. Zeratul swiftly slew it.