Titan Disease

"Nice of you to say, but you of all people should know...there's plenty wrong with me. Take my blood for example. I wish somebody would...this stuff is killing me!"

- The Joker in his last hours of life.

The Titan Disease is an extremely potent and deadly blood disease that originated from Dr. Penelope Young's research into the super-steroid, Venom and its powerful successor, the Titan Formula. This disease would ultimately claim the life of the Joker.

Arkham Asylum Incident
Although Dr. Young realized the dangers, Joker, who had been secretly funding the project as part of his own plans was determined to unleash an army of monsters upon Gotham City. Luckily, Batman was able to put a stop to Joker's plans before they could get that far - but not before the Joker injected himself with a large sample of Titan as a last resort.

Arkham City Incident
While in Arkham City, Batman was ambushed by Clayface (disguised as Joker) and knocked out by Harley Quinn. After he woke up, Batman discovered that Joker suffered from a horrible side effect of Titan which gave him a fatal disease that progressively killed him. At the time of Arkham City's final night of full operations, Joker only had a few hours left to live. Not willing to die without taking as many people with him as possible, Joker had his poisoned blood shipped to every emergency room in Gotham and the state.

In addition, Joker infected Batman with his blood as well to force the vigilante to find the cure for him. For the rest of the night Batman went through seemingly impossible odds to find a cure to save himself, his enemy and his city from certain death. Batman eventually found a way to create an antidote with the help of Mr. Freeze; the cure required a sample of Ra's al Ghul's blood. Just when hope was about to be in Batman's hands it was snatched by Harley who stole it from Freeze's safe while he was fighting Batman.

Seemingly cured of his illness while Batman was rapidly beginning to succumb to his, Joker put into motion his plan to stage a violent breakout from Arkham City. Determined to put a stop to the Joker's plans before he caused anymore death and destruction, Batman made his way to Joker's Funhouse at the Sionis Steel Mill where he finally confronted his arch-nemesis. However, before Batman could take the Joker down, they were interrupted by Hugo Strange's Protocol 10.

In the resulting explosion, Batman was pinned down by rubble, which left him vulnerable to the Joker, who planned to slit his throat. Before he could make good on his threats, Joker was interrupted by Talia al Ghul, who offered to take him to the Lazarus Pit where he could become immortal and all-powerful in exchange for him sparing Batman's life. Despite Batman's protests that Talia didn't realize who she's dealing with, Joker brutally knocked Batman out and the two then departed to the Lazarus Pit. Later, after he was freed from the rubble by Catwoman, and stopped Strange and Protocol 10, Batman made his way to the Monarch Theatre where he witnessed Talia seemingly kill the Joker with her sword through his back and out through his stomach.

Unfortunately, Talia gravely underestimated her enemy's cunning, and was brutally shot in the back in cold blood from behind by the real Joker who had been using Clayface as a decoy.

Batman and Clayface then engaged in a brutal fight to get the Titan Cure which Talia had stolen earlier from Harley and then dropped when she was shot. The Joker, still dying from his illness, used explosives to blow up the floor beneath Batman and Clayface's feet, which revealed that the Lazarus Pit had been hidden in the process. Still battling, Batman was able to eventually beat Clayface, retrieved the cure, and drank half of it, which cured himself. The Joker, meanwhile, was able to reach the Lazarus Pit and was about to dive in, when Batman used Talia's Sword to destroy the machinery, which was able to push Clayface into the Pit and destroyed it.

Batman eventually woke up and was taunted by Joker about killing Talia and poisoning Gotham, and Batman voiced his contemplation whether he should give Joker the cure or let him die to which Joker suddenly attempted to take the cure by force with a knife only for Batman to accidentally drop it to the ground, rendering it destroyed. After Batman revealed that he was going to give the cure to the Joker even after all his horrible acts, Joker started laughing at the irony before succumbing to his disease and died as his arch-nemesis watched.

Unfortunately, the cure only partially worked: it saved Batman's life, but due to being infected for a long time with a large amount of Joker's blood (at least four pints) it didn't really affect his body. While Batman's blood wasn't lethal like Joker's had been it was still contaminated, giving him hallucinations and mood swings until it developed into the Joker Infection. He eventually overcame the lasting effects through a combination of Scarecrow's Fear Toxin and his willpower.

Victims

 * The Joker
 * Batman
 * Poison Ivy