Birds of Prey meta: What if Harley has an unrecognized metapower to borrow luck from herself? That's how she can pull off things like the garbage bag bankshot or Mjolniring the baseball bat, but also happen to run under the window of a woman whose nose she broke.
In some DC Comics, the Joker displays a milder version of Deadpool's medium awareness, not just narrating and interacting with his own narration but also things like remembering un-canon events (like intercompany crossovers)
My headcanon is that the Joker is actually fully aware of the comic book in the same way that Deadpool or She-Hulk is, he just considers it vulgar to constantly mug for the 4th Wall. (Which is implied by She-Hulk a few times in the serieses where she's not leaning on it.)
The movie Harley Quinn did a leap of faith/trust fall into the same vat of chemicals that made the Joker the man he is, so if we assume it unlocked some ability to interact differently with the fabric of reality in him, it could have done so with a different twist for her.
If each time she digs deep and pulls off a nigh-impossible, billion-to-one shot, she's burning up the equivalent of Narrative Goodwill, it basically makes her a pulpishly exaggerated action hero: impossible shot in the clutch, followed immediately by a complication.
End result: she's simultaneously impossibly lucky and unbelievably cursed. So without having a cartoon body or "toon physics", she reads like a cartoon character in a non-cartoon universe.
