Lady Sevine and Archmage Allistarj pledged their allegiance with Razelikh. Another one also pledged his allegiance with Razelikh, Grol the Destroyer. Grol is the leader of the Dreadmaul tribe of ogres.
In exchange for their servitude, Razelikh granted each of them nearly unlimted power within the Blasted Lands. The amulet pieces are each attuned to the lifeforce of their owner, granting them immortality. As long as they remain within the Blasted Lands, they cannot be slain, their lifespans extended until the end of days.
Razelikh is an agent of the Burning Legion, who was stuck on Azeroth as the Dark Portal closed. Now that the Dark Portal has been re-opened, there is no telling what may happen, as of yet nothing much.
Shadowsworn mobs specifically at the Altar of Storms are known to have a bug that they wear what they drop. In other words, if a Shadowsworn Enforcer is wearing a hammer that looks like [Hand of Edward the Odd], instead of its normal two-handed sword, it has a good chance of dropping that. The same applies to all Shadowsworn mobs.
As of patch 2.0.5, the blood elves' and high elves' models were changed. Oddly, the high elves in the Shadowsworn cult are unchanged. They are supected to be the few last remaining high elves that use that model.