-Batcave-
Hulk and Batman walk into the Batcave and get to work on manufacturing the antidote to Titan, though Batman does most of the work while Hulk sits down to rest.
"How close are you to making the cure?" Oracle asks as the monitor reads 78% and slowly rises.
"Close. It's more difficult than we expected." Batman says. "The process is slow, difficult, and doesn't produce much antidote."
"And the good news?" Oracle asks, almost hesitantly.
"The chemical will definitely stop Ivy. It may also reverse the Titan transformation. I need to run more tests to be sure. I've set the computer to create more, but we need to get out of here and find Ivy." Batman says as he grabs a syringe filled with a bright green liquid.
"Thank God. Her plants have reached the Gotham River." Oracle says. Right on cue, several of Ivy's giant vines burst into the Batcave and destroy the monitors. "Batman! Hulk! Bruce! Are you guys all right?"
Luckily, Hulk and Batman manage to evade the vines as they block the main entrance. "We're fine!" Batman says. As the two heroes prepare for a final confrontation with Ivy and Joker.
-Later-
Sewers
As Hulk and Batman rush to the surface, Oracle rings up Batman. "Batman, Hulk, I've been running a simulation on the damage Ivy's plants will do if they reach Gotham."
"They won't get that far. The antidote will stop them and Ivy." Batman says confidently.
"I hope you're right. I'm here if you guys need me." Oracle says before cutting off.
-Main Sewer Junction-
The two heroes make it to the main junction, noticing a green liquid pouring down.
Batman rings up Oracle. "Oracle, we got another problem."
"What now?! Two-Face? Riddler? Some kind of giant Joker robot?" Oracle says in a whiny way.
"Ooh. Someone's cranky." Hulk remarks on Oracle's attitude.
"Unfortunately, nothing that simple. We're at the Main Sewer Junction, and it appears to be polluted with Titan. Why? What's he doing now?" Batman asks.
"I'll look into it." Oracle says more politely as she cuts the call.
After using their acrobatic skills to maneuver the sewer, Batman wonders aloud. "The Titan water seems to be corrosive, but it shouldn't trouble the suit or your boots, Hulk. Oracle, what have you found out?"
"Um...I'm not sure you guys are ready for this." Oracle says hesitantly.
"Try us." Hulk dares.
"Go ahead, Oracle." Batman says, ready for anything.
"Joker's pumping all the waste product from the Titan process into that chamber. It acts as a kind of natural storage tank. Once it's full, it releases the water into the Gotham River. Normally, it's safe, but..."
"But this time it's full of Titan. How do we stop it?" Batman asks, finishing Oracle's sentence.
"I'm working on it." Oracle says.
-Later-
As the two make it out, Oracle phones them up again. "Okay. According to the plans I have on file, there are three control rooms. The first is directly above you guys."
"We'll shut them all down." Batman says, to which Hulk nods.
"What will happen if this Titan stuff reaches Gotham?" Oracle asks, fearing the worst.
"It won't reach Gotham." Batman says firmly, ending the call.
-Later-
Pump Room
Hulk and Batman find the final control room, which is filled with Joker goons. Hulk grins as he leaps down and makes short work of them, punching and tossing them until they stop moving.
"Oracle. That's pump three disabled. We're going to head back up to the surface and stop Ivy." Batman says.
"Okay. Get in touch if you need anything." Oracle replies.
-Outside-
Out in the surface, Batman and Hulk rush to the Botanical Gardens, occasionally having to contend with snipers and more of Ivy's pod plants as her ethereal voice can be heard.
"I am everywhere. My babies know your every move. You and your kind are arrogant enough to think you can destroy us. You will fail and we will become the most powerful force on the planet."
Hulk rolls his eyes. "Forgetting someone?"
"You will pay, Batman and Hulk. For hurting my babies." Ivy continues to speak as Joker chimes in.
"Oh, God...Does she ever stop going on about those plants of hers?" Joker asks in annoyance at Ivy's monologuing.
"When I finish with Hulk and Batman, I'll be coming after you, Joker!" Ivy shouts.
"Will you really? Well, that's gratitude, isn't it? Women. You give them, presents, experimental chemicals and nice costumes, and they still turn on you. Well, good luck to you, toots. I've got an army, a city-sized dose of Titan, and a bag of weed killer. Come and find me when you're done with Bat-brain the gamma oaf. It'll be fun. You can bring the wine. I'll make the salad."
-Greenhouse Entrance-
Hulk and Batman make it into the Greenhouse and head towards Ivy. "So you're here at last. Do you like what I've done with the place?" Ivy asks teasingly.
"A bit." Hulk says in answer.
"Glad you like it, Hulk. My babies are growing, Batman. Come and see..." As the two continue to stroll further in, Ivy continues to taunt them. "Are you scared, Batman? You should be. You're only a man. And you, Hulk. Why fight this? Why fight me? Together, we could rule this world. Me as its queen...and you as its king."
"Tempting...but I'll pass." Hulk says as the two heroes reach Ivy's lair.
-Ivy's Lair-
They enter Ivy's 'home' as Batman approaches a vine. Before he can use his Explosive Gel on it, Ivy uses a nearby vine to knock the gadget out of his hand, startling the two heroes.
"I won't let you brutes destroy it." Ivy says confidently, underestimating the power the two heroes had.
"I told you to go to your cell." Batman firmly says as he clenches his fist.
"I was a fool. I thought the plants were in pain. Now I realize they were evolving, growing stronger!" Ivy says proudly as several vines burst through the floor and wrap around her.
"This looks bad..." Hulk mumbles as he clenches his fists, ready for a fight as the vines lift Ivy off the ground.
"And now we'll grow together!" Ivy yells as a massive flower-like plant emerges and 'consumes' Ivy, revealing her to be safely held inside the plant by a protective dome.
"Okay, this is really bad!" Hulk exclaims as the plant attacks the two, wrapping Hulk up in thick vines while it fires miniaturized spores at Batman, who easily dodges them as Hulk finally manages to break free from the vines and leaps onto the face of the plant and pries the protective dome open, exposing Ivy.
"Hulk! You wouldn't hurt me! Not after our night!" She pleads, trying to trick him into doing her bidding. "You don't want this! Deep down, you feel the same!"
"Ivy..." Hulk says softly, failing to notice a vine wrap around him and hurl him to the floor. "Damn it!"
"Don't let her trick you, Hulk!" Batman orders as the two heroes use their respective skills to fight and cripple the oversized plant. Hulk nods as he leaps up and tears off one of the tentacles that fire the spores, making Ivy and the plant shriek in pain simultaneously.
-Later-
With the plant unable to fight back, as Hulk had torn off all of its appendages, it falls forward, giving Batman the chance to deliver the 'killing' blow. He sprays some Explosive Gel onto the dome and as the plant rears back, he detonates it, making the plant reel around in pain as Ivy can be heard screaming in anguish. The plant collapses in front of Hulk and Batman and slides into the hole it originated from.
"Ivy!" Hulk shouts in protest as she falls.
"She's gone, Hulk! We have to go! Now!" Batman says, noticing the greenhouse beginning to collapse around them. Hulk nods as he grabs Batman and leaps out, leaving Ivy behind.
-Outside-
Arkham North
Once the two make it outside, fireworks explode in the sky, some of which form smiley faces.
"Datatata! Hulk and Batman! I know it's been a long, hard night, but good news! The party is about to start!" Joker says over a loudspeaker. "We've got everything! Music, dancing, chemicals that create monsters. You guys don't want to miss it. So get your asses over to the Cell Block, or you'll miss your final surprise."
-Visitor Center-
Hulk and Batman head over to the Visitor Center, coming across several Joker thugs, one of which is holding a clipboard.
"Guest list only! If your name's not on the list, you ain't going in!" The goon says as he reads the list of names. "Let's see. A, no, that's not right. B...Bane...Ah! Here it is. Batman. Next up! H...Harley Quinn. Nope, she's in lockup. Oh, here we are! Hulk." He says, showing that the clipboard has 'Batman and Hulk' spray painted across a blank piece of paper. "Hey! Looks like you're the guests of honor. Give them a big welcome, guys!" He says, letting the two heroes walk in as they pass a big congregation of more Joker thugs, which they quickly beat up before moving on.
-Visitor Room-
Batman and Hulk spot Joker sitting behind a plate of glass, strangely, a TV sits atop his head.
"Are you excited, guys? I mean, we've been building up to this point all night. Don't tell me you've not been looking forward to it. I know I have."
"That makes one of us." Hulk says in response as Joker pulls the TV off of his head.
"Surprise!" Joker says with glee. "Haha! Everyone always said I should be in television. You don't want to miss this. Really...it'll be a blast!" Joker says, putting the TV in the chair he was sitting in as he begins to count down from 10 as he walks away. When he reaches one, the TV explodes violently, dazing the two heroes, who weren't expecting that. Once they recuperate, Hulk and Batman walk through the hole the explosion left, eventually entering a room with Joker sitting atop a tower made of mannequins as well as two Titans sitting inside of cages. "Why didn't you stop them?" Joker asks the Scarface dummy as Hulk and Batman dispatch several Joker goons. "Me? It was your plan, you goofy clown!" Joker says, pretending to be Scarface as Hulk takes down the last of Joker's men. "Ahh, I'm sending you back to the Ventriloquest where you belong!" Joker says as he tosses Scarface onto the floor in frustration.
After this happens, one of the Titan creatures runs out of his cage and swings at the heroes, who are out of reach. "Bat...look. He's not a prisoner." Hulk says, noticing that the creature is wearing a torn up security vest.
"You both had to spoil everything, didn't you? Beating up Bane, feeding Scarecrow to Croc, slapping around Harley-my hobby by the way-and ruining all my lovely Venom plants." Joker says in disappointment.
"Well, technically, Croc ate Scarecrow himself." Hulk mumbles.
"It's over, Joker." Batman says.
"Over? Why, my dear delusional Dark Knight, it hasn't even begun!" Joker says gleefully as he pulls a lever, releasing the collars on his Titan beasts, who exit their cages and approach the heroes, joined by more ordinary goons.
"Here we go again..." Hulk sighs as he clenches his fists and roars at his monstrous opponents. As Hulk battles the larger foes, Batman slowly tends to the normal henchmen, punching and kicking them in the face and main torso while Hulk deals with the Titan monsters, trading powerful punches with them that practically shook the room. With one Titan down, Hulk easily takes down the second one, knocking it down and repeatedly bashing its face with his fists, though he held back, since it wasn't an inmate.
Once all the goons have been dealt with, Joker applauds the two victors. "Nicely done, boys. You deserve a prize! Your old pal, Commissioner Gordon." Joker says as Gordon drops in, hanging from a rope wrapped around his waist.
"What? Seriously, old man? Again?" Hulk asks in annoyance at Gordon's apparent incompetence.
"Say! He looks all run down. Let's pep him up!" Joker says as he aims his Titan dart gun at Gordon and pulls the trigger. Without hesitating, Batman jumps in front of the dart, which imbeds into his chest.
"Batman!" Gordon says in protest while Hulk's eyes widen in shock.
Batman pulls the dart out of him as his arm starts to pulsate. "Get away...!" He demands as he punches the ground, which cracks slightly. Joker climbs down from his tower and watches on with excitement as Batman struggles.
"Ooh, here we go! We're going to have some fun now, kiddies!" Joker says gleefully before realizing that Batman is fighting the transformation. "You're trying to resist the change?! That's not fair!" He says, kicking Batman in the face in an attempt to make him turn. "Come on! Give in!" He says, only for Batman to punch him in the face.
"Shut up, clown." Hulk says in annoyance as he looms over Batman.
"So, you wanna play hardball, Bats? Your call!" Joker says as he tries to tickle Batman with a feather, only to be shoved by Hulk.
"Oh! You're ruining my big night!" Joker complains. "Months of planning down the crapper...I just wanted to bring down your grim façades and for once let you guys see the world as I see it, giggling in a corner and bleeding. But you've both denied me even that." Joker says sadly as he aims the dart gun at his jaw. "I have nothing to live for." He says as he pulls the trigger, the force of the impact knocking him out cold. After a few seconds, Joker suddenly wakes up, gasping as his eyes glow a bright green as he slowly rises and begins to transform into a Titan version of himself. With Batman struggling to not turn, it's up to Hulk, who charges at Titan Joker, who easily stops him.
"What the-?" Hulk asks himself, surprised that Joker is able to stop him at all.
"So this is what it's like to be you...I love it! Hahahahaha!" Titan Joker cackles as he slams Hulk against the floor many times before throwing him against a wall and approaching Batman. "Let's take this upstairs, shall we?" He asks, backhanding Hulk when he tries to attack Titan Joker from behind.
-Later-
News helicopters hover above Arkham Island, searchlights scanning the island's infrastructure as Jack Ryder reports on the current events. "Arkham Asylum remains under lockdown, its staff at the mercy of the rampaging inmates. Less than ten minutes ago, we received this taped message."
"Greetings, Gotham. Joker here. Arkham is mine. Soon I'll unleash madness untold onto the streets of Gotham. But first, direct your eyes to the rooftops and witness the final destruction of your dear Dark Knight and your humble Gamma Goliath!" The message plays out.
"We've been circling the tower since-Wait! There! Joker is making his move!" Jack Ryder calls out as Titan Joker climbs to the top of the tower, holding a battered Batman in his right hand while Hulk lays at the bottom of the structure, struggling to stand after being manhandled by Titan Joker. As a helicopter's light shines on Titan Joker, he grins and looks at Batman.
"Showtime, Batman!" He shouts as he tosses Batman onto the ground, which has a spray painted picture of Joker's face. "Let's give the rubes something to talk about! A couple of freaks in a fight to the death!" Titan Joker says, gleefully jumping down into the arena and kicking Batman. "And for one night only, please welcome our special guest referee." Titan Joker gloats, directing Batman's attention to Gordon, who was now sitting in an elevated electric chair as Titan Joker grabs Batman again. "Come on! Change! Get crazy! It's the only way to beat me! You know you want to..."
Batman shakes his head in defiance. "Never!" He then injects the antidote into himself, much to Titan Joker's surprise.
"You wasted the antidote on yourself?" He asks as he hurls Batman against one of the electric walls surrounding the arena. "Now that's funny!" He giggles as he leaps towards Batman, who just barely rolls out of the way. "Hysterical! But still, you two spoiled my fun! And for that, I'll paint Arkham with your blood." Titan Joker says as Hulk leaps up into the arena.
"You want us? Come and get us, freak!" Hulk says as he helps Batman stand up. "Let's finish this, Bat."
Titan Joker grins as he swings his claws at Hulk, who grips his wrists and begins to squeeze. "I'm gonna kill you first, big guy. You're spoiling my fun!"
"You have a twisted definition of fun, clown." Hulk says as he kicks Joker's shin, throwing him off balance as Hulk headbutts him before shoving him back and punching him in the face hard.
"Ha! It'll take more than that to beat me, green bean!" Titan Joker says as he rubs his jaw, as if all of that barely affected him.
"Good. I love a good fight." Hulk says with a grin as he punches Joker in one of his exposed ribs, which hurt Titan Joker something fierce.
"Ahhhhh!" Titan Joker screams in agony as fresh blood pours from his rib. Hulk takes advantage of this, punching Titan Joker several times in the face and stomach while Batman fights some spare Joker henchmen, albeit slowly due to tiredness.
"Raaaahhhh!" Hulk roars as he pummels Titan Joker with unrelenting force. Despite being bigger than Hulk, Titan Joker was slowed down by his new body as Hulk keeps punching him. As this happens, Batman uses his detective vision, noticing an electric generator of some kind under the wooden floor.
"Hulk! Under the ground is an electric generator! Knock Joker through the floor!" Batman screams out as he takes down the last of the Joker henchmen.
Hulk nods with a grunt as he punches Joker in the gut, stunning him. "Game over, Joker!" Hulk remarks before uppercutting Titan Joker high into the air. When he hits the floor, he falls through it and lands on the generator, receiving high voltage shocks, though he cackles as this happens before it ceases.
Titan Joker coughs as he slowly climbs out of the hole. "I can take it. I can take anything you guys throw at me. You can't beat me. I'm actually going to win." Titan Joker says as Batman sprays some Explosive Gel onto his right fist. "Ready for the next round?"
"Always." Batman says determinately.
"What?!" Titan Joker exclaims.
"He said always, clown. Pay attention." Hulk remarks with a grin.
"We'll never let you win. Never!" Batman says as he and Hulk punch Joker simultaneously, making the Explosive Gel on Batman's gauntlet explode, sending the three combatants flying back as a result. Titan Joker groans before passing out as Hulk and Batman slowly rise, exhausted after a long night.
-Later-
Visitor Center
Oracle is talking to Gordon on a walkie talkie outside the Visitor Center as police reclaim the asylum.
"Dad! Thank God. I was so worried!" She says, happy to hear that her father is okay.
"I'm fine, Barbara. The GCPD finally has control of the asylum. Doctors are treating the injured, but it looks like it will take some time. All super criminals are back in custody. Heh. Quite a mess in there. And the Venom-enhanced inmates are returning to normal. Though for some, the process can be quite painful." Gordon says as Joker is reverted to normal, Ivy is rolled back to her cell and a former Titan monster reverts to his normal form.
"And Dad, how are you doing?" Oracle asks with concern.
"I'll survive. See you tonight, Barbara." He says, cutting the call as Hulk and Batman approach. "Shame about your car, Batman. Can I give you boys a ride?"
"Thanks, Jim, but we have one on the way." Batman says.
"Get some rest. You guys deserve it." Gordon says.
"You bet we do." Hulk says tiredly as Gordon's police scanner goes off.
"All units, all units, the Second National Bank was just robbed by Harvey Dent, aka Two-Face. Two officers down, and the suspect is fleeing in their patrol car."
"Stay safe, Jim." Batman says as he and Hulk enter an enlarged Batwing, which easily holds the two heroes, despite Hulk's weight as it flies towards Gotham. As the Batwing soars above the water, a crate of Titan floats along the water as Bane's hand grabs onto it.
-Epilogue-
Wayne Manor
Bruce Wayne's Room
Back at the relaxing and luxurious mansion, Batman goes to his room and gets out of his shredded and filthy suit, changing into some comfortable pajamas as he goes to sleep, clearly needing his beauty sleep after all the craziness that he and Hulk went through tonight.
-Hulk's Room-
Meanwhile, Hulk stares out the window of his room, sighing in relief that it's all over when he hears a very familiar voice.
"My love?" The voice inquires. Hulk spins around, seeing Wonder Woman standing outside his room, a silk robe wrapped around her slim and curvaceous body as she smiles at him.
"Diana!" Hulk exclaims, running over to her and hugging her tightly.
"Oh!" Wonder Woman exclaims in surprise as she hugs him back. "You okay?"
"Just hug me..." He pleads as he hugs her for a full minute before releasing her.
"What's wrong?" Wonder Woman asks.
"I...have to say something." Hulk says as the two sit on his bed. He sighs as he tells her about the nightmarish hallucination Scarecrow forced him to go through at the asylum, to which Wonder Woman gasps in shock. "I'm scared, Diana. What if that wasn't a hallucination? What if it was a...a premonition?"
"My love..." Wonder Woman says softly as she holds his hand. "You could never hurt me...or the others. Our love is too great for such a thing to even be possible. Your heart is pure, so it could never happen. Besides...I have some news of my own to tell you."
"What is it?" Hulk asks, to which Wonder Woman smiles as she gently places his palm to her stomach.
"I'm pregnant...with your child." She says as she smiles wide. Hulk's heart practically explodes with joy and happiness.
"Really?" He asks, receiving a nod from his lover.
"Yes. Your child. Our child." She says happily as the two kiss.
"I'm so happy..." Hulk says, forgetting about his hallucination as he and Diana lay down on his bed together. "So, what is its name?"
Wonder Woman smiles as she gazes into her green-skinned lover's eyes. "It's a beautiful baby boy. As for his name, I'm thinking...Atreus Banner-Prince."