Book of Destiny

"I've traveled far to this place and time to lay this precious burden at your feet. Use this book to reshape the world as you see fit. Show them what a real god can do, John." "Why me?" "You have vision. That book holds the key to your transformation, John, and all you have to do is open it. Use it wisely, John. The universe is in your hands."

- Mar Novu and John Deegan

The Book of Destiny was a metaphysical book that gives a worthy individual the power to alter reality, until Oliver Queen destroyed its powers.

History
At some point in the past, the Book of Destiny was bestowed by Mar Novu to individuals of different Earths across the multiverse to test them for a crisis, to which Novu claimed to be beyond his abilities, by letting the chosen individuals create their own Elseworld.

On Earth Ninety, a struggling Barry Allen attempted to take hold of the Book of Destiny, but stopped short when Mar Novu retrieved it instead. Mar Novu then presumably proceeded in altering Earth Ninety's reality, to which Barry made his escape.

On Earth One, Mar Novu chose John Deegan as the book's owner. Deegan opened the book, where he saw all of reality and, using the book, made the first change to reality.

The Flash and Green Arrow
After John Deegan created his first Elseworld, the only change in reality he made was swapping Oliver Queen's and Barry Allen's realities. The change only affected Earth One, and did not affect Barry and Oliver's memories. After seeing Novu give the Book of Destiny to Deegan in Cisco's vibe, Oliver speed-sketched the scene, tracing the scene to Gotham City.

John Deegan then hid the Book of Destiny in a dislodged part of a wall in Arkham Asylum. After being confronted by Oliver and Diggle, Deegan retrieved it during his escape, only to be blown away by Supergirl's super breath. The book is then brought to A.R.G.U.S. for Felicity, Curtis, Caitlin and Cisco to analyze it. Their analysis showed that the lock of the book is not only cryptographic but also metaphysical in nature. Barry Allen of Earth Ninety then breached inside the building and revealed the true purpose of the Book of Destiny, before Mar Novu appeared to them in public.

After being confronted by Barry, Oliver, Kara, and Barry from Earth Ninety who he teleported to somewhere, Novu gave the Book of Destiny back to Deegan and the doctor altered reality once more, and on a larger scale than the last one.

Superman, hero of Central City
After John Deegan was ordered by Mar Novu to "think bigger", he created his next Elseworld, and the following changes to reality were made:
 * Due to book's limitations, Deegan was only able to alter the reality of Earth One.
 * Barry Allen and Oliver Queen are known and feared, even by other criminals, in Central City as the "Trigger Twins", notorious for having a bank robbery spree, and are the CCPD's highest priority. Their memories from the original reality are still intact, but neither of them are speedsters.
 * Malcolm Merlyn, Joe Wilson, and Ricardo Diaz are police officers of the Central City Police Department.
 * John Deegan stole most of Kara's powers, leaving her with a weaker version of her abilities, and became Central City's superhero known as "Superman".
 * His base of operations is in S.T.A.R. Labs, where Killer Frost, John Diggle, and Alex Danvers work as his agents.
 * The time vault is now called the Fortress of Solitude.
 * He got the idea of taking on Clark's appearance when he saw the event of Clark taking on A.M.A.Z.O., which was the only record of him being on Earth One.
 * He created a history where "Superman" once fought a villain named "Bizarro".
 * Kara Danvers was known by the Elseworld denizens to have done something horrible, and thus was locked in the pipeline of S.T.A.R. Labs.
 * Cisco Ramon is a criminal who breaches inside banks and steals their money and the owner of a criminal bar.
 * Gary Green is a bartender working for Cisco.
 * Jimmy, James Olsen's Earth One doppelgänger, is Cisco's bodyguard, who often kills anyone for his boss.

Later, Barry, Kara, and Alex headed to the "Fortress of Solitude" to retrieve the book. The book was found unlocked in the time vault. Kara opened the book and tried to change reality back herself, but the power of the book proved too much for her. Barry then stated that Clark knows how to use metaphysical books, to which Kara grabbed the book and found Clark being bested by Deegan. Kara used her heat vision to throw the counterfeit Superman into the sky and gave the book to Clark. Clark then used the book to return Kara's, Barry's, and Oliver's powers and abilities, and attempted to revert reality, when they were hit by Deegan's thunderclap, who escaped with the book.

Deegan, once more, let the power of book change reality to his liking, causing panic in Central City. Clark finds Deegan and tries to talk him out of his actions, only for him to summon A.M.A.Z.O. using the book, who locks in combat with Brainy. Using the light-generating hammer in the Fortress of Solitude, Lois Lane struck it to the ground, blinding Deegan and setting him off-balance, only to quickly recover the book. Deegan then directed the book's power towards Clark, knocking him off and hitting Lois who was struck high into the air. Oliver managed to make it in time and attempted to shoot Deegan with metaphysical arrow given to him by Novu. Deegan reacts to this and tries to hit Oliver with the book's energy, only for the book to be shot instead, filling it with too much energy, which caused to book to implode, frying the book, its powers and John Deegan. The loss of the book's powers then reverted reality back to normal.

Former powers
"I can see everything." "And a word of advice: think big."

- John Deegan and Mar Novu


 * Metaphysical connection: The lock of the Book of Destiny only shares a metaphysical connection whomever the book deems worthy to use it and letting the individual unlock it. With Novu's abilities, the book can also be recalled into his possession.
 * Reality manipulation/Elseworld creation: Once opened, the book allows its user to manipulate reality to how they see fit in the blink of an eye. This ability of the book was used by Mar Novu as a test to see if the denizens of the created Elseworld would be good enough to be able to survive an oncoming crisis.
 * Absolute reality perception: Once opened, the book enables its user to look at the whole of reality.
 * Ergokinesis: The books allows its user to release surges of energy powerful enough to even harm Kryptonians.

Former weaknesses

 * Universal limit: The user of the book can see and change the events and reality of only the universe that the user is currently on.
 * Energy overload: When Oliver shot the Book of Destiny with a powerful arrow of metaphysical nature, the book absorbed too much of its energy and imploded, toasting the book and its powers.

Trivia

 * The symbols in the book appear to be the same ones as the ones used by Nora West-Allen to write in her journal, as well as the ones that Barry Allen wrote in after returning from the Speed Force.
 * In the DC comics, the Book of Destiny is also known as Book of Souls and belongs to Destiny of the Endless.