House Brokengulf rose to noble status in Waterdeep in the mid 1200's DR. Over 100 years later, the family's wealth was lost nearly to the point of bankruptcy at the hands (claws?) of the ancient green dragon of Kryptgarden Forest, "Old Gnawbone."
This is a telling of that tale, as remembered by Belcoria:
Perhaps one of the most elaborate stories told to warn of the trickery of Unknowns is that of Claugiyliamatar and the Waterdhavian noble Saerlin Brokengulf. It begins with her feeding on the herds of cattle owned by the Brokengulfs in the grazing lands north of Waterdeep and east of her forest lair. Saerlin made known he would pay a bounty to any who might halt these attacks.
So the green dragon employed magic to disguise herself as a Unknown, "Arguylt Yamaliac," (spoken with such heavy accent the anagram is easily lost). Arguylt offered to drive away the green dragon for a hefty price. The dragon then used her crystal balls to track the location of this payment, and destroyed the house, devoured its guards, and stole the coins. She then flew back to the ranch and using illusions portrayed an epic battle between silver and green dragon before witnesses. For fun, she included smashing the rancher's fences and frightening livestock to flee into open grasslands (for her dessert!)
As the battle came to the end, the combatants vanished over the mountains, disappearing from its selected audience. The "victorious silver dragon" then perched on top of the Brokengulf's manor, demanding payment (which of course was already stolen) for successfully defeating Old Gnawbone. Lord Brokengulf had to scramble to find alternative funds (as the silver dragon made it clear the alternative was to lose the house). Here, the silver dragon flew away, barely able to hold aloft the Brokengulf boat plucked up from the harbor and crammed full of coins.
After a tenday hiding this and the rest of her horde in the mountains, Old Gnawbone then reappeared at Brokengulf Towers as herself -- angry and demanding twice the payment made to "Silver Slayer Arguylt" to spare the lives of the entire Brokengulf family. (So - this would total 4 times the silver dragon's fee - since the original payment had been stolen (1), then the payment in the boat (+1 = 2), then this demand for twice the payment (+2 = 4)!
When Lord Brokengulf played for time (trying to hire a wizard to blast away his dragon troubles forever), Claugiyliamatar toppled the grandest tower of the villa down into its garden, crushing three of Lord Brokengulf's sisters and crippling Saerlin himself. Though it left House Brokengulf with nearly nothing, the dragon got her payment, flying back to her cave, after wrecking the rest of the villa almost as an afterthought.
Old Gnawbone then set all the traps and ambushes of Kryptgarden Forest, and made herself conveniently absent from the woods, anticipating retribution. Indeed, the nobles of Waterdeep, upon hearing the plea from the Brokengulfs, agreed to assemble a strike force and vanquish this trouble-making dragon in a show of strength to deter this sort of thing from happening again.
But the crowning stroke of cruel genius in Claugiyliamatar's elaborate plan was her timing of the whole affair to coincide with a challenge for control of her forest-lair by a rival green dragon from the High Forest named Endracritar. Having used her crystal balls to carefully watch his bold but extremely careful plans for an overwhelming and decisive attack, she was able to avoid this pesky matter by ensuring when the force sent by Waterdeep entered her forest looking to defeat a powerful green dragon, they sure as heck would find one!
Despite being well-prepared with the magics and devices meant for Old Gnawbone, Endracritar was no match for the fury of the assembled mages and heroes of Waterdeep. Yet no treasure horde of any significance was located and the group returned to the City of Splendors empty-handed except for an excellent epic dragonslaying story. With no more resources to call upon and the attention of the city turned to fresh matters, Claugiyliamatar's quiet return to Kryptgarden Forest drew no further attention.