Finding out that Harley Quinn is actually a Legacy Character is just loaded with this. The character fans remember is a blonde psychiatrist in Arkham Asylum who tried to analyze the Joker and ended up turning into his Monster Fangirl. Was that character the very first one or were there others before her? Sure, she seemed to have stayed alive for a long time but, for all we know, she was killed off-screen and replaced with a lookalike. How many fan-girls has the Joker had?
On the other hand, if it is the same one, he suggests the name to her as a play on her own name, so it brings to light whether or not he was planning to kill her in their meetings.
However, that's only if the Joker's taken at his word on that point - for all we know, he just murdered a bunch of women, threw Harley in a cell with their corpses, and made that up as a way of "testing" her. There would've been some evidence of this beforehand, and Bats would've used it to try to convince Harley to turn away from her life of crime. It's more likely just a sick joke from the Joker to spite Harley for replacing him with Deadshot.
...That actually makes perfect sense! "I'm dead for 5 minutes and you f*ck some Billy the Kid wannabe? Fine! Maybe I'll make you think you're replicable!"
Considering that the New 52 universe is a 5-year timeline for Batman, it wouldn't seem likely that Joker had so many sidekicks in that shot of amount of time. And even if he did, wouldn't Harley have heard about at one point or another?
Wait, so The Joker spent a year faceless? How did he pull that off? The point of skin is to protect the body from disease and other things. So how did Joker spend a year missing his face without getting infected?
There are other ways to protect the face. Perhaps he kept it covered with bandages or a face covering and used eyedrops to keep his eyes from drying out.
If we're supposed to accept that a chemical bath of undetermined contents bleached his skin, dyed his hair and stretched his face into a grotesque grin, pretty much this.
We also have Hush as a precedent, though he didn't spend a whole year faceless.
Wouldn't the skin from Joker's face have wasted to dust and he have grown a whole new layer of skin over his face within a year?
There's nothing saying he doesn't have a new layer of skin. It's not addressed either way, and it wouldn't affect anything if he did have some new skin. Given that his own blood is poisonous, who knows how much of his physiology has changed during his exposure to all those chemicals.
The skin from Joker's face (that he cut off) was kept in a freezer.
When Catwoman encounters the Joker, she acts all "Never heard of you." Either she was insulting him or she was being serious. As one review pointed out, it would be unbelievable that she's being serious, because she had worked with Joker and other villains from time to time. So how is it possible for her to never hear of someone when she worked with that someone at one point?
This was most likely a dig at the "new" appearance of the Joker. With the face mask & all.
Harley Quinn bites off Joker's tongue and spits it out. His ability to speak is not affected at all! How is this possible?
The same way he cut his tongue in two during Batman R.I.P. and could still speak.
Although the implication in RIP was - although Morrison had to clarify this - was that Doctor Hurt (an entirely unnatural being by that point himself) was the only one who could understand Joker at that point.
Tim states that Jason is the closest thing he's ever had to a brother. What the hell about Dick?! Did the New 52 completely erase all the adventures and moments the two shared before the reboot?
That may very well be the case, since Dick and Damian already have a close bond that is touched on. Playing relationships off each other isn't surprising in any ensemble.
Yes, actual relationships that have been developed, not ones purely informed. Battle for the Cowl still happened, so Jason still brutally kicked Tim's ass. You don't get past that with a few favours.