This prayerbook, along with anything written on its pages, can’t be damaged by fire or immersion in water. In addition, the prayer book doesn’t deteriorate with age. It contains prayers and hymns to the god Hades. Inside the pages are also pearls of advice about how to navigate life and how to accept the gift of death when it's time. On the back page there is a map of a river that you can't quite understand. 

The Word of Hades grants disadvantage on constitution saving throws and death saving throws to those that are considered hostile towards you as long as the following conditions are met: You use your bonus action to sing Death's Hymn and you are in possession of the book. 

The book also has spells stored within the pages. As an action, you may cast one of these spells directly by reading the associated prayer or hymn out of the book. You may use each spell 1 time per long rest without consuming your own spell slots or material components. As such, you do not need to be a spellcaster to use these spells.

Spare the Dying - Cantrip - You touch a living creature that has 0 hit points. The creature becomes stable. This spell has no effect on undead or constructs.
Gentle Repose - 2nd level - You touch a corpse or other remains. For the duration, the target is protected from decay and can't become undead.
See Invisibility - 2nd level - For 1 hour, you can see invisible creatures and objects as if they were visible, and you can see into the Ethereal Plane. Ethereal creatures and objects appear ghostly and translucent.

The book's features and spells will not work for Aasimar of gods other than Hades unless they've dedicated themselves to him. It also not work for Clerics unless they are dedicated to Hades. Those who disrespect Hades, or the gods in general, will find themselves cursed with disturbing visions which will impose exhaustion after a rest is taken. 

Notes: Disadvantage: Constitution Saving Throws, Disadvantage: Death Saving Throws, Exhaustion, reading the pages for the minimum of a short rest by someone who isn't dedicated to another god