That sums up the relationship between the World's Greatest Detective and the most well-known villain in all of comic-book lore. Scott Snyder understood this best when he wrote The Black Mirror, a story in which Bruce Wayne is believed dead and Dick Grayson assumes the role of Batman. But the Joker instinctively knows he's a fake, and crawls into a sewer, incapacitated by his grief, posing no threat to anybody.
The challenge is the mercurial nature of the character himself: the Nolanverse Joker as portrayed by Heath Ledger is a very very different character from most Jokers that had come before (more deliberately calculating, less zany). Since Ledger's performance, the comic book version has definitely turned darker as well: he's always been murderous and there have been portrayals in which he's done very gruesome things (The Killing Joke, for example, in which he shoots, strips, tortures, and photographs Barbara Gordon as a means of getting at her father), but since 2008's The Dark Knight, he's become not only a symbol of violent anarchy, but a regular butcher as well. Very different from the prankster I grew up with, but interestingly, a return to his grim mob roots in the 40s.
All of which make it difficult to reconcile his wackier side.
And yes, I paired him with Harley Quinn (I couldn't not!). Harley never made it into the Nolanverse (and even if Ledger had not died, it's unlikely she ever would have), but I absolutely felt that if I'm going to do comic book characters, these two had to be together. And poor Harley's had a mess of a history since Paul Dini created her for the Batman Animated Series in the 90s, so she deserve a little love here.
For her portrait I didn't use any particular actress, but I wanted to include one head with the harlequin hat and one without (which is her modern look these days). She's the only character in this paper doll series who didn't exist in my childhood, so she's a little out of place and won't have any Bronze-Age groovy outfits, but we'll find interesting things to do with her nevertheless.