Re Harlequin
Several characters going by that name (OTTOMH, a villainess who wore a conical cap, ruff, tutu, and striped tights and ended up marrying Green Lantern Alan Scott. An illusion casting villainess who wore a purple and white body suit with a diamond motif, and tried to woo Scott away from his wife. And I think I’m forgetting somebody) by that name have been around for years. They have nothing to do with this, so just forget I mentioned them.
But reaction to the Harley Quinn of the cartoon was great enough that she was made canon in the graphic novel Harlequin. She had her own ongoing title for a while.
She is nearly identical to the character from the animated series. However, an injection given to her by Poison Ivy (who, just like in the cartoon, becomes Harley’s best friend) rendered her immune to toxins, and unexpectedly gave her slightly superhuman levels of agility, strength and speed. Harley was also given more history and personality. After getting into college on a gymnastics scholarship, and exchanging sex for good grades. Harley managed to get a job as a therapist at Arkham (these details match the animated version). However, the comics reveal that Harley’s plan was to treat the Joker and the other famous criminals for a few years, then write selfhelp books and get her own talkshow. Instead, she fell in love with her Mistah Jay.
Harley is also obsessed with the idea of true love and sees herself as a matchmaker. She avoided killing two detectives who were after her, because she was convinced that they were destined to fall in love. After throwing a bomb behind them, she watches them jump off a balcony and says to herself ‘That’s it! Take her hand! Yes! Now, in a moment of life-affirming joy, kiss!’
Harley realizes that her relationship with the Joker isn’t healthy. However, one of the reasons the Joker abuses her and keeps trying to kill her is because he really does love her. He isn’t used to caring about another person, and his feelings for Harley frighten him.
Harley’s comic was bizarre, whimsical, homicidal and a great showcase for her. Then, a new artist decided to make things dark and gritty and a new writer decided to make the comic hardboiled detective noir, mob wars, and international espionage. It sucked beyond words. The series was cancelled. Harley still turns up in other series and has a miniseries with her and Ivy out now.