The Covenant of the Lost are the remainders of the souls of dead members of the Shadow Pact or other sub-factions. Their souls return to the Dark Demiplane as eerie shadow monsters that are but an empty shell of their former selfs. Tamara was the first to become such a creature.
All members are direct or indirect members of the Shadow Pact.
See: Gurshy Rockpool, Frogfolk, Covenant of the Lost, Fellowship of Fellows, Forsaken, Order of the Forgotten, Order of the Guardian