"By the moon’s pale light, I sing my mournful tune,
A soul bound by sorrow beneath the lagoon.
My voice calls the weary, the lost, and the bold,
But my embrace is chilling, my heart long turned cold.

Born of betrayal, I dwell in despair,
Once human, now cursed, in the water’s snare.
Beware my song, though it soothes like a balm,
For beneath lies a fate that shatters all calm.”

Who am I?