Darbel Montrose <Shadow Council Warlock> is a level 39 elite rare mob human found roaming with a minion in Stromgarde Keep in Arathi Highlands. Considering that the only known Shadow Council presence within Arathi is that of the Argus Wake, which is also in league with the Syndicate she fights alongside, it is reasonable to assume that Darbel is in fact one of its secretive agents.
Banish (Shadow) - Banishes an enemy, preventing all action but making it invulnerable for up to 15 sec. Only one target can be banished at a time.
Curse of Weakness (Shadow) - Reduces the Physical damage dealt by nearby enemies for 2 min. Only one curse per warlock can be active on any one target.
Shadow Bolt (Shadow) - Hurls a bolt of dark magic at an enemy, inflicting Shadow damage.