My campaign, "Beneath the Pinnacles of Azor'alq" (BPAA), is a 3.5e D&D World of Greyhawk message-based game (Play-by-Post) set beneath the surface of the Dramidj Ocean. Feel free to take a gander at the campaign background, by following the link in my signature below.
One of the PCs is a half-dragon (topaz) succubus, using half-dragon rules from Draconomicon and monster level progression from Savage Species, though technically her mother is a succubus and father is a topaz dragon (can't have a creature created from two templates, as that would leave no base creature, and fleshing out a half-fiend/half-dragon in 3e got messy). As my campaign is set beneath the surface of the sea and topaz dragons can breathe underwater, I decided to grant the PC the aquatic subtype. The character's mother was firmly rooted in the campaign's history, while her grandmother is the main protagonist NPC. Here's an excerpt:
"Over time, Zephra wrought an unholy alliance, starting with her children, the fiendish fey; fruition of her dalliances with nymphs and nixies. Her magically-grafted forearms, an unwitting offering from the topaz dragon Pazos, had gifted Zephra with the ability to both breathe and befoul the waters around her. As she took shelter in the hidden world beneath the waves, the half-fiend continued to research the arcane interactions between the artifacts of Al'Akbar and the circles of stone, while aware that the lair of Pazos was now within her grasp.
It was known to Ariss that Pazos kept his lair in an undersea cave located in the region of the Janasib isles. Within this air-filled cavern, the dragon secreted his hoard; including a collection of magical pearls, an untold wealth in coins of silver, gold, and platinum, and a handful of treasures of artistic value. Among the latter, the dragon kept an ornate tapestry. It was this tapestry which interested Ariss, for she knew what Pazos did not. Depicted upon it was the lost treasure fleet of Tharizdun, now lost beneath the waters of the Oljatt Sea. This much did the dragon reveal to his demonic temptress. This fleet, Ariss knew, carried the dire tome known only as "Lament for Lost Tharizdun".
The succubus had tried in vain, years before, to wrest the location of his lair from Pazos. She gave the dragon a daughter, yet still he held his tongue. In time Ariss grew weary of the dragon's games. After casting their child into the sea, she dispatched the dragon and severed his forearms. These she grafted onto the mangled limbs of her alu-demon daughter, in an arcane ritual which imbued her with many of the dragon's powers and memories.
Sending her fiendish fey to collect the hoard of Pazos, Zephra sought the means to travel to the faraway Oljatt Sea."