And Roxy Rocket made her DCU debut last month.

Why does DC hate Tony Isabella so much?

Well, Lady Lunar was in the comics long before she was in JLU.
And Tsukuri was based of Katana(She was changed alot, but still)

She was in many ways the antithesis of Harley Quinn, since her backstory was that, as Molly Maynne, her imposing 6′ height and athletic prowess scared all the menfolk off, as did her fierce independent streak. Working as Alan Scott’s executive assistant, she took up as the Harlequin largely because she figured that by facing GL as an equal she might win him over as just that. And thanks to Roy Thomas in the 1980s, she finally did, with the result that they’re currently married.

The Joker’s sidekick Harley Quinn has very few similarities to the Golden Age Harlequin aside from the name, which I suspect was chosen primarily because it’s about the only synonym for clown that easily lends itself to being feminized. Harley is a subordiante, sidekick character with no exotic weaponry as with Maynne, and with a costume that’s not in any way similar to the 1940s character’s.

I wondered the same thing myself when I first saw Quinn on B:TAS — I’d already heard of the 40s version by then — but within her first line or two of dialogue on the show it was clear there was no inspirational link between Alan Scott’s self-proclaimed “loving enemy” and the Joker’s codependent “hench-wench.”

Superman: TAS created a villain called Livewire who also appeared in a crossover episode of Batman, in which she teamed up with Harley and Ivy against Batgirl and Supergirl. She only recently made her first mainstream DCU appearance. Another Superman: TAS villain, Volcana, appeared on Justice League, but has not appeared in the comics.

In Justice League, they created Long Shadow, Wind Dragon, Juice, Shifter and Downpour – collectively known as the Ultimen. They were analogues for Super Friends characters Apache Chief, Samurai, Black Vulcan and Jayna and Zan, the Wonder Twins. None have appeared in the mainstream DCU (nor have the Super Friends characters, save Zan and Jayna).

(It’s also worth noting that Black Vulcan was intended to be the DCU character Black Lightning, but H-B created an “original” character to avoid paying creator Tony Isabella. Also, Samurai can be seen as an analogue for Red Tornado, and another character, El Dorado, has similar powers to the Martian Manhunter.)

There are two other villains I only recall seeing on Justice League, and never in the comics – Tsukuri and Lady Lunar – but I’m not as certain on the two of them.

On another Super Friends tip, the original junior sidekicks to the Super Friends, Wendy and Marvin, recently made their mainstream DCU debut in Teen Titans – only about 30 years later!

No Wonder Dog or space monkey, Gleek, as yet!

To my knowledge, none of the original characters created for Static Shock (including Soul Power, another Black Lightning analogue), Batman Beyond or Teen Titans have yet appeared in the mainstream DCU. All three series debuted many significant new characters.

Further on the “no Black Lightning characters ’cause we’d have to pay Tony Isabella” tip is JLU’s villain Steven Mandragora, an analogue for Tobias Whale.

Finally, in the last season of Justice League Unlimited, DC requested that the series stop using Aquaman and related characters. As such, planned Black Manta appearances were replaced with a new character called Devil Ray, who has not appeared in the comics.

Superman: TAS created a villain called Livewire who also appeared in a crossover episode of Batman, in which she teamed up with Harley and Ivy against Batgirl and Supergirl. She only recently made her first mainstream DCU appearance.