Actor Allusion: When Femme Fatale challenges the Powerpuff Girls to name some memorable female superheroes, Bubbles mentions Supergirl and Batgirl. Bubbles's voice actor, Tara Strong, voiced Batgirl in The New Batman Adventures some time earlier.
Banned Episode: The season 5 "See Me, Feel Me, Gnomey" was rumored to be banned in the US, due to the heavy use of strobe effects (which would have triggered epileptic seizures in more sensitive viewers, much like the notorious Pokémon episode "Electric Soldier Porygon." Reportedly, it was banned for allegedly having Communist undertones, but this was never proven). The episode can now be seen on the complete series DVD set for the show and on the complete series collection on Netflix. It aired in Canada on March 18, 2004.
The official reason for the banment in the US, according to Craig McCracken himself is because "[the network] claimed that the metal beams in the destroyed buildings looked too much like crosses and one of the hippies looked like Jesus. That was never our intention at all, we were really surprised that they banned it."
Box Office Bomb: Warner Bros' marketing for the movie was quite lousy (as stated in the main page), but CN did their part and promoted it to heck and back (even [adult swim] got involved). Outside the channel, however, there was barely any mention of it. Not helping was it was pitted against Men in Black II on the opening weekend, was overshadowed by the surprise hit Like Mike and Warner Bros focusing their campaign on the Scooby-Doo live-action movie. As such it preformed poorly. Because of this, the series finales for Ed, Edd n Eddy and Codename: Kids Next Door were scaled back to made-for-TV fare rather than made into feature films and the Samurai Jack was stuck in Development Hell for decades before being abandoned in favor of the 10-episode revival.
Creator Backlash: While she stands behinds its message, Lauren Faust has said that she wasn't happy with how "Equal Fights" turned out, feeling that feminism was too dense a subject to depict in a lighthearted cartoon. It didn't help that she'd had to endure complaints from pretty much every side of the argument, from real man-hating feminists to men accusing her of misandry.
Descended Creator: During seasons 5 and 6, Don Shank and Charlie Bean lent their voices to their caricatures. Shank had the most appearances (including the 4th season premiere "Film Flan").
Earlier, Craig McCracken voiced the narrator on the Whoopass Stew shorts. Lou Romano voiced the Amoeba Boys (and the father bird on "A Very Special Blossom" during season 2) on said short.
Development Gag: The designs of the Run-of-the-Mill Girls from "Oops, I Did It Again" were based on redesigns Craig McCracken came up with after the early pilot received negative test audience reactions due to the girls' bug-like designs.
In Memoriam: The episode The City of Frownsville was dedicated to those who were killed during the events of 9/11, which happened just before the episode aired.
Keep Circulating the Tapes: "See Me, Feel Me, Gnomey" has never been shown in the U.S., not even in the current runs on Boomerang. It is on the complete series DVD set and on Netflix, though.
The original What-A-Cartoon era shorts had Ernie Anderson (best known as either Ghoulardi or the longtime announcer for ABC, as well as the voice of The Love Boat and the syndicated run of Break the Bank (1976)) as the narrator, but died of cancer in 1997, before the series went on the air, so Tom Kenny took over the role.
Likewise, Bubbles and then-unnamed Ms. Keane were both voiced by Kath Soucie in the What-A-Cartoon shorts, but when the series went on air, Tara Strong and Jennifer Hale took over the roles, respectively.
Carlos Alazraqui provided Lil' Arturo's voice in his first appearance. In all other episodes, Arturo is voiced by Tom Kenny.
Cristina Hernández (Blossom) and Rossy Aguirre (Buttercup) voiced Lime and Cherry respectively, two girls from another trio of super-powered girls living with a guy, except their personalities are different between the two series.
Also, Cristina Hernandez, along with Enrique Cervantes (Mojo Jojo) and Sergio Gutierrez Coto (The Narrator) voiced Catwoman, Bane and Batman respectively. That's right, The Narrator is the The Dark Knight and he's fighting against Blossom and Mojo Jojo!
Fingerless Hands: Former Trope Namer (the trope used to be called Powerpuff Girl Hands). One of the most notable aspects of the Powerpuff Girls' character designs is that their hands lack fingers and thumbs.
So Once Again, the Day Is Saved: Nearly every episode ends with the Narrator saying "So once again, the day is saved thanks to the Powerpuff Girls", with occasional variations.
Unisex Series, Gendered Merchandise: Word of God is that the series was aimed at a unisex audience. Despite this, almost all merchandise is aimed at girls and women. This was taken to its natural extreme when the series received a Magical Girl anime and the 2016 reboot was explictly aimed at girls.
Before the Girls, Craig played around with a luchador superhero character as the star for his thesis film, but after drawing a birthday card for his brother with three cute, Margret Keane-inspired girls, he though the idea of those little girls fighting bad guys was hilarious and chose that instead.
Buttercup was originally named Bud.
The original tone of the cartoon was meant to be much more adult (it was called "The Whoopass Girls" after all). One can only imagine what that series would've been like if Craig hadn't made it more kid-friendly.
One planned episode, Deja View, about the girls visiting an alternate universe ruled by their evil versions, ended up being cancelled due to the visuals requiring the budget to go overboard (which they were already stretching). It wound up being given to the comic book writers and turned into the 50th issue.
As said on the main page, Craig wanted Jack Black to voice the Gnome in "See Me, Feel Me, Gnomey", but they couldn't due to him being too busy and expensive.