Dallah Thaun, the Lady of Mystery, is the dark aspect of Yondalla. Physically split off from Yondalla when she created the halfling race, Dallah Thaun is worshipped both as a deity in her own right and also as a part of Yondalla. Anyone who worships one goddess worships both, and prayers to are heard by both. Each Goddess knows everything the other knows and is privy to the other's plans. Since they both work towards the same goal -the benefit of the halfling race- they do not quibble over one another's methods. Instead, the two goddesses utilize each other's strengths and compensate for each other's weaknesses.
For example when someone evil harms a great number of halflings, Yondalla's followers nurture the survivors while Dallah Thaun's seek vengeance. Likewise, the Blessed One provides her people with food, comfort, and healing, while the Lady of Mystery helps them find wealth. Should any dirty work need to be done, it falls under Dallah Thaun's purview, and Dallah Thaun is said to receive the souls of dead halflings and guide them to their final reward.
There is no inherent evil in accumulating wealth; indeed, a nest egg for one's golden years, when a hard-working halfling can no longer work as hard, is a necessity. How one gains this wealth is another matter. The Lady of Mystery does not condone killing or even harming others for money, but relieving the overly wealthy of a portion of their burden is quite acceptable. In fact, any method that harms no one is fine with Dallah Thaun so long as the perpetrator doesn't get caught. Secrets, guile, lies, half-truths, flatter, intrigue, manipulation, and all things done by stealth are the purview of Dallah Thaun. "Don't get caught" is her credo, and the lesson that she passes along to all her worshippers. Dallah Thaun also serves as an avenger for any wrongs done to her people.
Very few outsiders know of Dallah Thaun's existence, and the halflings like to keep it that way. Since she is an aspect of Yondalla, halflings who venerate her can truly say that they worship Yondalla who, as everyone knows, is a lawful good goddess. Since no one except halflings realizes that Dallah Thaun exists, she is not as powerful as her other half. In many ways, the two goddesses epitomize the dichotomy between openness and secrecy that is so characteristic of halflings.
The Lady of Mystery appears as a beautiful female halfling with dark hair and eyes. She dresses all in black and wears a voluminous black cloah with a hood that conceals her face. She tosses a gold coin in her gloved hands.
Clerics of Dallah Thaun are chosen by senior clerics of both Yondalla and Dallah Thaun. They covertly watch the young people in a community and identify those who have the mind-set and talents for Dallah Thaun's service. They begin to groom those individuals as clerics even without even telling them they are being trained. The candidates are sent on covert missions, told secrets and bade to keep them, and provided with opportunities to participate in confidence games. When the secret of their training comes out, they may either accept Dallah Thaun's service or refuse it with no stigma.
The Lady of Mystery's followers often undertake quests that involve stealing from the rich, discovering secrets, and acquiring particular items through means other than force. If halflings are in trouble with a local lord over thefts that have occurred while they were camped on his lands, Dallah Thaun's followers are the ones who enter the lord's keep by night and suggest that harming or expelling the halflings could result in the revelation of the lord's affair with a certain young noblewoman destined to marry another.
Prayers to Dallah Thaun are usually whispered or mumbled, and they often sound like the kind of wishes one makes while daydreaming. Typical prayers begin "If only I could get a hundred gold pieces," or "if only I could get out of this place safely," or "If only I could figure out how this trap works.'
Dallah Thaun's shrines are usually surreptitiously folded into Yondalla's. For example, a temple to Yondalla in a halfling town might have a shrine to Dallah Thaun behind a secret door or a sliding panel. Similarly, a family shrine to Yondalla in a wagon might have a rotating panel with Dallah Thaun's symbol on the other side. Dallah Thaun's clerics celebrate the same holy days as Yondalla's do, and they are usually present for the same celebrations. They also bless new ventures, successes of any sort, newly acquired wealth, thieves' tools, and other "tools of the trade."