Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
The Dee Dees are Harley and Ivy's granddaughters
Harley and Ivy somehow made babies together using science. They do have red hair like Ivy.- Jossed: Those are WIGS to make them look like dolls, not actual hair.
Alternatively, the Dee Dees are Harley and Jack "The Creeper" Ryder's granddaughters
Creeper was a Stalker with a Crush towards Harley, and his personality while not under the patch is similar enough to the late Mr. J's without the psychopathic tendencies for Harley to give the guy a chance. Jordan Pryce became Paxton Powers' cellmate
It seems more than coincidental that Bruce Wayne had not just one but two sleazy, sociopathic, backstabbing business partners who had both secretly planned to kill Bruce.Joker's plot to kidnap and brainwash Tim was a result of the events of "Wild Cards"
Joker's defeat at the climax of that episode, in addition to being his final chronological DCAU appearance before the flashback here, was a particularly humiliating one: Having Batman turn his pet Mind Rapist against him, shooting to spit his so-called Insanity Immunity and leaving him even more off the deep end than usual, and all on live TV to boot, thanks to him buying the airways so that Ace could use her powers on the entire country. Unfortunately, Ace's assault on Joker's mind only left him even more crazier than usual, and blaming Batman for Ace turning against him (he was the one who revealed that Joker still had the immunity headband to her) and still having the other Cadmus tech he liberated when breaking out Ace and the rest of the Royal Flush Gang, decided to do to Robin a physical version of what Batman had Ace do to him as payback.- Alternatively, Batman and Ace proved that Joker was actually not insane but evil. Remember, the only reason he wasn't given the death penalty is because the courts thought he's just misguided and thought it's possible to reform him. Now the truth comes in and the entire country now sees Joker as a parasitic being that had to be exterminated.
The Joker always knew who Batman was, he just never cared
He likes to make a big deal and show out of it, but he revealed that in the end he was disappointed at the revelation, perhaps the Joker had always known the truth, he had a theory or an inkling but never fully cared as the point was never about who Batman was. It was always about the games, the fight, the final punchline, he once said if you have to explain the joke there is none, perhaps knowing who Batman was, was the explanation to the joke. It never once mattered who Batman was under the mask, all that mattered was that he was Batman. Hence his disappointment once he knew, he'd play it off as "crying for mommy and daddy" being the disappointing bit, but the truth was that now that he knew, the punchline carried no more weight.Tim Drake was also dosed with the same chemical that made Clayface
Tim actually physically transformed into the Joker’s look when the Joker chip was active, with a significantly different appearance to Tim (such as the pointy chin. It’s possible that part of the Joker’s experiment included dosing Tim with the RenuYu chemical to make that possible, just using the chip to signal the change, which would make what happened to Tim all the more tragic since his greatest tragedy as Robin prior to this had come at Clayface's hands.