Elyssa's violent death and the betrayal of the man she was going to marry prevented her from resting, and her spirit became bound to the lake as a seductive rusalka, drowning any man who was foolish enough to enter her water. Learning how to free the rusalka from Piotyr and Magda, the Paladin Hero learned the spirit's name from her gravestone in the graveyard. Granted some knowledge of her life, her memories flooded back to her. She gave the adventurer some of her hair for him to weave into a hand broom. The Hero took the broom with Elyssa's hair in it to beat the grave of her fiance. Elyssa felt the moment Janos' was defeated, as she began to decay. The Hero then had to grant her truest desire -- to be kissed by a Hero. After her wish was granted, she vanished -- finally free.
Her gravestone remains, reading:
"No effort could Elyssa save;
She passed into a wat'ry grave.
Her body was lost;
Only her memory remains."
Elyssa is a character in Quest for Glory IV: Shadows of Darkness. Though all of the Hero classes can meet Elyssa and should befriend her by giving her flowers, only the Paladin is able to free her spirit. The rusalka is actually a fairy from Slavic mythology, though she is not an undead in those myths.