Corrupted Mementos

Corrupted Mementos are used to unlock research at the Titanic Research Archive in the Chamber of Heart and for buying items from Wrathion.

Source
Corrupted Mementos can drop from corrupted mobs as well in Ny'alotha, the Waking City and from Vision of Orgrimmar and Vision of Stormwind and rewards from quests and chests.
 * Crate of Cursed Mementos
 * A Hand in the Dark