Isidora, Voice of the Dead is a boss in Blasphemous. To unlock this boss, 30 bones must be given to The Collector NPC on Albero's Ossuary.
She is seen briefly emerging from the flames of a censer at the Albero Ossary as a naked woman with fiery hair, that will shortly afterwards materialise a set of ceremonial clothes and a scythe formed from the Severed Right Eye of the Traitor. Upon her death, her clothes and hair will vanish, the censer and scythe will break and she will attempt to pick the Eye from the ground, before finally collapsing and being reduced to ashes.
According to the relevant item descriptions, she was once a songstress that would delight the Albero children with her songs. One day, the Miracle manifested as she was singing, making the dead in the graveyard sing in reply to her. Entranced, Isidora entered the Ossary where the combined voices of all the dead joined and mixed with her in a lugubrious chant, referred since to as the "Voice of the Dead".
At some unspecified point after the sealing of the Fourth Visage, the High Wills entrusted Isidora with guarding the Severed Right Eye of the Traitor, which shaped itself into a scythe, giving her control over fire and the ability to fly and teleport.