|This requires cleanup. Reason: Needs past tense, in-universe POV, references
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A Moonwell was a magical well in the Moonshae Isles, sacred to the goddess Earthmother. There were several Moonwells but the most important was at Genna Moonsinger's druidic grove in Myrloch Vale. The Earthmother was able to manifest her power through the Moonwells. If corrupted by dark magic or filled with corpses, Moonwells become Darkwells which could be used to summon or create evil creatures or as portals to evil dimensions.
In the Year of the Saddle, 1345 DR, firbolgs polluted the Moonwell to allow the Beast, Kazgoroth, to enter the Forgotten Realms. The beast was killed with the sword of Cymrych Hugh, and the well was afterwards cleansed by the goddess.
In the Year of the Bloodbird, 1346 DR, an army of undead captured the Moonwell in Myrloch Vale. The goddess used her power to spray milk from the well, saving her druids from death by turning them to stone. However, the Moonwell became so polluted that Bhaal was able to manifest through it, and use it to create perytons, an owlbear, and a displacer beast from the bodies of animals lured to the well.