Orbital bones deal contact damage equal to Isaac's damage at the time it was spawned, repel enemies that touch it, and will block 3 shots or deal 2 ticks of contact damage before being destroyed.
Bonies deal 8.3 contact damage and 5 damage with thrown bones.
Black Bonies will explode on death, dealing 40 damage to enemies it hits. The explosion will not hurt Isaac, but can push him.
Internally, the Book tracks each position an enemy was killed in the current room, and uses those locations as spawn points for bone orbitals and Bonies; using the book gives a **high probability** for each location to give one of them.
If one of these locations doesn't give a bone orbital or bony, it can still give one if the book is used in the same room without leaving. However, once a location gives something, it cannot do so again.
Using the book in a room that had no enemies or was re-entered does nothing and expends the charge.
Orbital bones occupy the same area around Isaac as Blue Flies, meaning Isaac can have an incredibly dense ring of bone orbitals around him that nullifies most attacks.
Having a large amount of blue flies can create gaps in the ring of bone orbitals that leave Isaac vulnerable in those spots.
Friendly monsters killed in the current room can also be used by Book of the Dead.
Destroying black poop will damage the friendly Bonies acquired from this item.
Concept art for "Reanimate" (misspelled as "Reanimte"), an early version of Book of the Dead, on the right side along with other Booster Pack items and trinkets, by Edmund McMillen.
The Book of the Dead has been added in Booster Pack #5, after the initial release of the DLC.
The Book of the Dead is a collection of ancient Egyptian funerary texts made out of papyrus, consisting of magic spells intended to assist a soul's journey through the Duat (underworld) and into the afterlife.
The quote "Rise from the Grave" is a reference to the beginning screen of the video game "Altered Beast".
Bug! If sufficiently many bone orbitals are created, other familiars may disappear. Collecting a new familiar or resuming the run will restore the missing familiars.
4 rooms 
Defeat Delirium as The Forgotten
Baby-Bender: No effect.
Car Battery: Since dead enemies can be animated only once, Car Battery does nothing.
Contagion: Poison effect can spread to and kill friendly Bonies.
Duct Tape: Only affects orbitals.
Mystery Egg - Spawn three charmed enemies in the same room.
Bug! If sufficiently many bone orbitals are created, other familiars may disappear. Collecting a new familiar or resuming the run will restore the missing familiars.
The Forgotten Unlocks 
The Binding of Isaac: Rebirth 
Achievements
Attributes
Bosses
Cards and Runes
Challenges
Chapters
Characters
Co-op
Items
Item pools
Monsters
Objects
Pickups
Pills
Rooms
Seeds
Transformations
Trinkets
