Ryndala Merendil

Lady Mirabelle Merendil was a traitor to Cormyr. She attempted to use the first apprentice royal magician, Amedahast]], into aiding an assassination attempt on the young Azoun I. Her assassins were defeated by both Amedahast and Azoun I, and she quickly fled Cormyr afterwards. She died sometime afterwards and was interred under an unknown tree, becoming the fifth Ghazneth.

Ghazneth
As a Ghazneth, Lady Merendil had the power of disease, causing a feverish plague to sweep around her, sapping the strength and will of her opponents. Even if her enemies survived their encounter with the deadly demon, the plague weakened them enough that the Ghazneth could quickly overwhelm them later on.