As I understand, every Dark Knight from the dark multiverse incarnates a specific fear and regret of Bruce Wayne of Prime Earth, as some Knights of the Dark Multiverse have living through some events previous to the Rebirth, we should assume that some events are born from the fears of Bruce Wayne of New Earth.
Here's a list of every Dark Knight I founded and wich fear it represents, some of this fears are available in the character's article, the ones that are not are based in my own opinion. Some elements from the list are going to be seen a little forced because of the little known about his backstories, but well, I tried my best. The last ones of the list are not actually members of the Dark Knights but I still counted them, as they also represents some of Bruce's fear.
The Batman Who Laughs: Bruce's fear of being just as bad as the Joker, how much affected him his long war against him, and his regret that he can't stop the Joker without killing him.
The Devastator: Bruce's fear of losing hope, how important his friendship with Superman is, and both the fear and regret that he cannot fully trust the Man of Steel.
The Drowned: Bruce's fear of going too far in the fight against superhumans, his love for Catwoman, and his inability to trust anyone but himself.
The Dawnbreaker: Bruce's fear of how dangerous he would be with superpowers, but lacking his adult discipline, his inner despair taken to its extreme, and his regret over his inability to move past his parent's deaths.
The Red Death: Bruce's fear of losing members of the Bat family, his love for them and regret for those he failed, and the fear of old age slowing him down.
The Merciless: Bruce's fear of what he would become if he started killing, how Wonder Woman helps him see the good in others, and his regret that he can't end his crusade since his villains keep coming back.
The Murder Machine: Bruce's fear of not being as self-sufficient as he thinks when it comes about: His technological dependence to fight his biggest foes; His father-son relationship with Alfred and how much of himself can be affect by the possible loss of this; And the regret of cutting off other people.
The Grim Knight: Bruce's fear of using gunfire.
Ark: Bruce's fear and regret that he might not be better than the people he leaves in Arkham, consider his crusade against crime is pretty much an obsession and a problem.
B-Rex: Bruce's fear of never being strong enough to stop the criminals for real and regret that the only permanent solution he can think of is killing them.
Bathomet: Bruce's fear of end up causing an terrible menace because of his arrogance.
Batmage: Bruce's fear of becoming too far by learning magic and regret that he didn't get a proper training to face big magical threats.
Batman who frags: Bruce's fear of never being resistant enough and of what he woudl be by being unstable and rebelious.
Batmanhunter: Bruce's fear of being too focused on his war and regret of dragging other people into the conflict.
Batmazo: Bruce's fear of not being able to adapt and deal with every possible menace.
Black Monday: Bruce's fear of being ignorant, impulsive and insensitive.
Chiroptor: Bruce's fear of being a "toxin" and "pollute" the people.
Darkfather: Bruce's fear of being evil and regret that he can't drive people into the light.
Kull: Bruce's fear that his love for Diana might have been a mistake.
The Pearl: Bruce's fear after reading Thomas Wayne letter from Flashpoint that were his parents the ones left with the mantle of vigilante, as being Batman is something he wouldn't desire for anyone.
Quietus: Bruce's fear when recruited Duke Thomas of having him suffer the same cruel fate as Jason Todd.
Warbat: Bruce's fear and regret that his obsession of fighting crime might become a serious problem in his life in times of peace.
Doctor Arkham: Bruce's fear and regret that he might be patronizing the madness by leaving people in Arkham's sanity-breaking hands.
Baby Batman: Bruce's fear of his aces-in-the-hole and his willingness to keep fighting crime end up as simple child's play (His tricks and gear proving useless).
Batmobeast: Bruce's fear of his reliance on excessively armed vehicles and regret that his obssesive crusade turned him into a vigilante.
Batom: Bruce's fear that his cautioness might stop him from being effective.
Batrocitus: Bruce's fear of having his inner rage and hate to turn him unstable and uncontrollable.
Beyonder: Bruce's fear that having a successor in his legacy, as he doesn't want anyone else to be "Batman".
Castle Bat: Bruce's fear of never being able to leave Gotham and regret that he can't change the city his parents loved for good.
Collector: Bruce's fear and regret that the cautioness and the need of knowledge of every possible problem might be bad for the others.
Mindhunter: Bruce's fear of being too paranoid about people's secret and regret that he can't fully trust in aliens, such as Kryptonians, Czarnians, Martians and Tamaraneans, over his dangerous powers.
Night Glider: Bruce's fear that his inhability to fly by himself might be hinder in his vigilantism.
Robin King: Bruce's fear that he was always broken deep inside, and that the death of his parents was ultimately just an excuse for the darkness and violence that was always inside of him.
The Broken: Bruce's fear of failing at taking back the Batman mantle.
Saint Batman: Bruce's regret of choosing Azrael as his sucessor and fear that Azrael's way of being Batman might have been the best for Gotham.
Batman the silenced: Bruce's fear of descenting to madness due to his parents' death.