Paul Dini had found a gold mine when he blessed comics & cartoon fans with Harley Quinn (Arleen Sorkin, Days of Our Lives) during season 1 of Batman: The Animated Series. Not content with casting Harl as the on-again-off-again girlfriend/partner of The Joker (Mark Hamill), Dini saw a means to expand on Harley's world.
In "Harley & Ivy", the Clown Prince of Crime is in one of his worse moods, and sends Harley packing. This wouldn't be the last time this would happen, but it just so happens that Harley makes good on her promise to prove Joker wrong and become a big shot crook in her own right. It just was a matter of finding the right partner, namely, Poison Ivy (Diane Pershing). The two cross paths when each tries to rob a museum, and, finding common ground, join forces.
Here's how they met:
Small wonder, then, that 17 years later, Dini was asked to write a pair of Bat-centric books for DC. Gotham City Sirens showcased Harley & Ivy, along with Catwoman, with Riddler, now operating as a PI on the side of the law, as a male foil. Dini wrote the first couple of issues, then left to concentrate on Streets of Gotham. Both series should still be running if not for DC's insipid New 52 initiative in 2011.
"Harley & Ivy" gets an A.