Halcalya is about average height for her race. Her undead state is rather well-preserved, since she did not spend too much time dead before being risen into the Scourge, but a few bones can be seen sticking out here and there. Her leftover skin is a deathly grey, typical for the Forsaken. Her hair is dyed a rich purple, to add color to hair that in life had turned white with terror at some point. Her eyes shine with the same eerie yellow glow typical of the Forsaken.
When ungeared, she prefers to wear blue, and lots of it. Near her shirt's neckline, she wears two pins, one carries the insignia of the Argent Crusade, and the other carries the insignia of Occupy Azeroth.
Halcalya carries herself rather calmly, and often shows more in common, emotionally, with living humans than with Forsaken. This has caused her to deviate from the usual "hive mind" resolved mentality of most Forsaken. She attributes this to the type of person she possibly was in life, though she remembers nothing of it.
She fears the Forsaken's reputation in the Horde is being tarnished by rogue elements in high Forsaken ranks, and longs for lasting peace not only with the Horde, but also with the Alliance. This longing has led her to form her protest group Undercity Underground, and join the Argent Crusade. She still holds banshee queen Sylvanas Windrunner in high regard, but feels the Dark Lady is being manipulated by the Royal Apothecary Society to turn the Forsaken into "Scourge 2.0".
Halcalya Marxworth was born in Brill around the time of the first war, back when Lordaeron was still a human kingdom. She and her older sister Bretanya were born into a family of well-to-do scribes going back for generations. Her sister rejected the family profession and moved to Stormwind as a teen, but Hallie stayed in Brill, receiving the training to make her into another family scribe. On the side, she also took training as a warlock. Not much else is known of this area of her life, as public records from old Lordaeron didn't go into much more detail.
Hallie and her parents were not able to flee Tirisfal when the plague hit. As a result of the plague, Hallie and her parents fell ill and died from the biological agent, and were soon after raised as mindless Scourge. It is not known what happened to the elder Marxworths, but Hallie was one of the ones who regained sentience via the efforts of banshee Sylvanas Windrunner, who broke from the Scourge and soon after would form the Forsaken.
Hallie's memories upon regaining sentience had been destroyed save for one: her first name. Fearing that her last name had been something just as needlessly fancy, she made up a short surname, Dalan. As "Halcalya Dalan", she expressed unwavering support for her Dark Lady, and started to make her way in the world. Feeling the embrace of shadow energy, she correctly concluded she had been a warlock in life, and resumed her class training.
In the years to come, however, she felt something was not quite right with what was going on with the Forsaken, and tensions began to flare between Hallie and her battlemate partner, Taekk. After noticing her battlemate hadn't reported for a couple months, Hallie broke off on her own, and started doing her own investigations into current events.
After The Shattering, Hallie started to do some digging into the events surrounding Wrathgate, the war with Gilneas, and the goings-on at the Sludge Fields. In all cases, she had come to one conclusion: the Royal Apothecary Society likely were the true ones pulling the strings at the Undercity, and their actions were detrimental to the well-being of the Forsaken. In reply, she formed a protest movement called the Undercity Underground, and started active recruiting in Orgrimmar and Brill. This has caused her to be unpopular in the Undercity proper, and as a consequence she rarely visits there anymore. She aso joined the Argent Crusade, as their goals were similar to hers regarding the Forsaken and the state of Azeroth in general.
Shortly after joining the Argents, she held audience with Highlord Darion Mograine of the Knights of the Ebon Blade on behalf of her movement. Mograine informed her that her sister was an Ebon Knight under his command. Hallie set up correspondence by personally stuffing a letter into the mailbox at Goldshire (Bretanya's last-known location), and later met her sister at the crypt at Brill's cemetary.
Having gotten the gist of her life information from her sister, Hallie decided she would reclaim her old identity back, despite her lack of remembrance, inspired by discovering family outside of the Forsaken. She has since reclaimed her original surname and restarted her inscription training.
She continues her movement to educate the public about the Royal Apothecary Society. She is in the process of converting one of the Southshore inns into her headquarters, and continues to try to recruit new members to the cause, expanding it to support the removal of corruption in all factions under its new name "Occupy Azeroth". She and her sister are the main Horde and Alliance contacts, respectively, for the cause.