Updated: Jul 6, 2019
There's some explanation needed. The Batman who laughs is an alternate version of Bruce Wayne from the dark multiverse who was infected by the joker toxin and recruited by the dark god Barbatos and was thought dead, but was actually in the custody of Lex Luthor. How He got his hands on him I have no idea.
The Batman who laughs gives some exposition about how Lex can only reach his true goal if he chooses to lose it all. For some reason Lex lets him go which makes the joker leave the legion of Doom. That's right. The joker is afraid of this guy. It's because the Joker doesn't want him and Batman's conflict to end because he feels like him and Batman can't live without each other and the things that Batman who laughs wants to do to Batman isn't funny at all to even the joker.
The main story picks up with Batman pursuing a train with some armed robbers on it. They're easily dealt with since, well, it's Batman. He opens the carriage to see Bruce Wayne's dead body. This is a dead Bruce Wayne from another Earth and Batman immediately makes the connection that this is the Batman who laughs. This is the work of someone who's both smart and insane.
We then cut to Arkham asylum where the joker is being held in intensive care under maximum security. Two guards are just talking when Batman shows up and slices these two guards with what looks like a freaking lightsaber.
This isn't actually Batman though and this is an alternate version of Batman known as the Grim knight who's a version of Bruce Wayne who shot his parent's murderer when he felt remorse for killing Bruce's parents.
He's here to assist in the Batman who laughs in the killing of the joker. The Batman who laughs just rocks up and splits the joker's head. Obviously, The Joker wasn't actually there and the person who was killed was just a stand in. Meanwhile, the joker is trying to break into the Batcave and surprisingly, Batman just lets him in. The joker unsurprisingly pulls a gun on Batman but then shoots himself and reveals why. His heart is filled the joker toxin and he knows that the only way for Batman to stop the Batman who laughs he must too become the Batman who laughs.
Batman doesn't want to become the Batman who laughs. The Batman who laughs is everything that Bruce Wayne despises. He starts injecting himself with every variation of the Joker Toxin cure that he has in a desperate endeavour to prevent his transformation.
The Batman who laughs is still killing Different versions of Bruce Waynes from every earth in the dark multiverse and it's all in a bid to create a serum that will turn anyone exposed to it into a *insert name here* Who laughs. Luckily, Batman has found something that was set up in Gotham city in the 1700's which Batman calls the last laugh protocol. If the city were to be infected by the plague then this protocol would have the city cut all ties and make sure that it would have enough food and water to live it out. If this new Toxin that the Batman who laughs is making is exposed to the people then this protocol would shut down the city in order to keep the citizens safe.
The Batman who laughs goes to Wayne Enterprises to stop this protocol but is confronted with Batman. They fight but The batman who laughs gives the order for the Grim knight to shoot and disable Batman so he can carry out his plan.
The Grim knight had actually sabotaged the least laugh protocol days ago and he wants the building to implode. He succeeds and the building is obliterated. Batman returns to the Batcave to ask a barely living Joker what the Batman who laugh's plan is and the joker explains that not even he knows. The joker explains that the only person who might ,as he's studied the Gotham sewer system, is James Gordon's son: James Gordon Junior.
He'd been suffering from psychopathy for years with plans to take down Gotham via the sewer system but has been taking specialised drugs to fight back the psychosis. Only problem is that Batman doesn't want this stable version of James Gordon junior because this joker toxin infected Batman needs someone unstable.
Unfortunately, the grim knight swoops in and kidnaps James Gordon senior as we simultaneously learn that there's still a fail safe protocol for the last laugh protocol. This protocol can only be activated by Bruce Wayne ,which they have two of, and James Gordon senior. The Batman who laughs always knows what Batman/Bruce Wayne is thinking because The Batman who laughs is also Batman/Bruce Wayne.
Batman has realised that nothing is working and locks everyone including Alfred out of the Batcave. Alfred finally gains passage into the cave and discovers that Batman is welding something. A replica of the Batman who laughs's helmet.
This is when we find out how the visor works. It's made of dark metal from the dark multiverse that allows the wearer to see the deepest fears and urges of those around him. It's so he can learn what the Batman who laughs is planning and where he's going to strike next with the high concentrated levels of joker toxin that he's manufactured.
Batman uses his visor to travel an alternate reality in the dark multiverse to a version of black gate prison run by a version of Bruce Wayne who's immediately killed by the Batman who laughs in disguise as a prison guard an convinces the other guards that Batman is the Batman who laughs since he's wearing the helmet of the Batman who laughs. At the same time James Gordon junior has thrown away his medication and the grim knight has set the jokers who laugh after Jim Gordon senior.
Luckily he's rescued by his son Jim Gordon junior. Meanwhile, Batman is using the dead Bruce Wayne as a meat shield to escape the guards firing armour piercing rounds at Batman. That's when Batman starts using the visor to respite the addresses of the guards to scare them off.
While this is happening The Batman who laughs has been visiting the court of owls to ask them for assistance in enacting his plans to release the joker toxin. They say no because the know who this is and the know that they need to kill him before they do anything. The talons are sent to kill the Batman who laughs but reveal themselves to have been literally disarmed.
He kills the member who he was addressing him and calls out that he was here for another Bruce Wayne. This version of Bruce Wayne is the version that took control of the court of Owls and used them for his own nefarious means.
They have a fight but it's not really shown if the batman who laughs kills him as he's most likely got plans for this version but there's most likely no escape for this Bruce Wayne. Meanwhile, Batman has taken the James Gordon junior and senior to the Batcave to enact the last laugh protocol. This is when Batman realises that it was too easy. The batman who laughs wanted all of them in the Batcave.
The Batman who laughs sends Batman a message and just starts constantly taunting him on whether he should activate it or not. Batman can either hope that it works or just find a different way that could eat up more valuable time that they don't necessarily have. Batman just activates it as the Batman who laughs explains that Gotham had always been structured to be a place for the rich to triumph over the poor.
Batman just activates it admitting that everything he's tried to help Gotham hasn't worked. Luckily, this is all part of the plan because Batman knows that when the protocol was activated the grim knight would have full control over the power grid which would allow him to do what he did to his Gotham city to this one. Batman now has a plan to once and for all beat the Batman who laughs. The batman has been using dark metal to transport these dead Bruce Waynes and Batman uses this knowledge to foil one of the batman who laughs assassination attempts on another Bruce Wayne.
Batman continues to contemplate the fact that he's the most unhappy version of Batman and pretty much the worst version. Luckily Batman has found a way to bait the batman who laughs to Wayne manor. Meanwhile, James Gordon junior and senior have been tasked with distracting the grim knight. They find a blast from the past/future to beat the grim knight. prototype Batman beyond
Batman and the Batman who laughs are just throwing down like there's no tomorrow and the Batman who laughs is confident since he knows that our earth prime's batman is the worst version of Batman. Batman is struggling as he's technically only got 5% of his cells that haven't been taken over by the joker toxin. That's when Batman pulls the youngest and happiest version of Bruce Wayne out of the multiverse in an attempt to once again bait the Batman who laughs but that's when the Batman who laughs pulls his ace in the hole. The batman who laughs explains that he's gone far beyond Bruce Wayne because bats are the only mammals to have evolved past their own kind. They learned to fly.
That's when he reveals that the happiest Bruce Wayne there's ever been was the one that finally drove himself over the edge. That's our Bruce Wayne when at this point he was fully transformed into the Batman who laughs.
To be continued...