Rashomon Style: In one episode, the Mayor is kidnapped by Mojo Jojo and blindfolded. The girls save the Mayor and beat Mojo Jojo, but can't stop laughing after. The Mayor asks why. The girls each tell the story of how they saved the day today differently, accompanied by Art Shifts. What they neglect to mention? The Mayor was naked all along.
Reality Ensues: Everything related to the town of Citiesville, most notably the girls' destruction of the bridge leading in to town to stop some robbers. The bridge was both the only way for workers to commute to Citiesville and a historical landmark, costing over three million dollars. Reality Ensues, and hard.
Reunion Show: 2008's "Powerpuff Girls Rule", a PPG special made five years after the show ended, featuring nearly every main character within the series, as well as all the original voice actors.
Rhyming with Itself: In "See Me, Feel Me, Gnomey", this trope is rather egregious when the PPG join in Professor Utonium's "Freedom Beef" song, as they rhyme "peace" with itself rather forcefully, directly after rhyming "powers" with itself.
Rogues Gallery: Mojo Jojo, Fuzzy Lumpkins, The Gangreen Gang, Him, Princess Morbucks, Sedusa, The Rowdyruff Boys to a lesser extent and The Amoeba Boys if you consider irritation to be roguish. Rainbow The Clown has also appeared in the background in his villainous mime-form post-Mime for a Change
The comic book story "Steal A Meal" (Cartoon Network Block Party #26) has the girls doing a tearful Big "NO!" upon learning that after all the breakfast cereal in town had been stolen the only thing left was oatmeal.
Space Is Noisy: The few times the girls go into space, they can communicate with each other just fine.
Spear Counterpart: The Rowdyruff Boys, Brick (red color scheme), Boomer (blue color scheme), and Butch (dark green color scheme) to the Powerpuff Girls, Blossom (pink color scheme), Bubbles (cyan color scheme), and Buttercup (green color scheme).
The girls can fly faster than the speed of light. At top speed, they have been known to bend the time-space continuum and perform Time Travel, thus creating an Alternate Universe where there has been no Power Puff Girls to save the day for fifty years.
Gangreen Gang member Lil Arturo temporarily gains this ability in "Power Lunch".
One of the later criticisms of the series was that the show promoted animal cruelty because of their treatment of Mojo. Episode 57 ("Save Mojo") depicted a group of animal rights activists protecting Mojo from the girls despite their argument that Mojo is an evil animal and therefore others must be protected from him.
Two episodes featured the Smith family, one member of which was their angry teen son Bud. The first episode, Bud's entire appearance consisted of him yelling something typically teenagerish at his father, such as "I hate you!" and "No one understands me!" The second episode, which features the entire family as villains, provides every member of the family with a motivation for why they hate the Powerpuff Girls - and Bud's is "You know what? I hate everything!"
Also, the Gangreen Gang. Literally.
Teeth Flying: Bad guys' teeth go flying in the opening sequence; also, one episode is pretty much based on this trope - Buttercup learns the Tooth Fairy gives you money for teeth, and starts deliberately knocking villains' teeth out and collecting them to make a huge windfall.
Too Dumb to Live: The mayor. In one episode he jumped out a window because Bubbles told him to go save the day... while pretending to be him.
Took a Level in Badass: Bubbles in "Bubblevicious" to prove she's hardcore. She even subverted her apparent chickification when Mojo captured her and gave her the full blunt of his torture device before she broke out and beat him mercilessly all by herself. She only softens from her tough exterior when her sisters finally admit that she's hardcore, only to slide right back into it when Mojo tried to make a cheap shot at all three of them.
Twist Ending: The episode "HIM Diddle Riddle" revolves around the girls flying around town, trying to solve HIM's insidious riddles in a desperate attempt to save Professor Utonium, only to fail, and now HIM is going to make the professor PAY!... full price for breakfast. The ending is such a big wtf, that the narrator just stumbles, "And once again, the day is... um... yeah..." while the girls just float there staring blankly.
Ultimate Evil: HIM, as actually stated in one episode. Most of the episodes with HIM simply revolve around the girls surviving HIM's magic and psychological challenges.
Unfortunate Implications: Touched upon In-Universe. In the "Members Only" episode, Major Glory talks the girls through several gender roles, asking who does various things ("Who goes to work?", "Who pays the bills?", etc) and receiving "Our Dad" as an answer each time. Then he gets to cooking and cleaning, getting the same answer. 5:12 - 5:45
Major Glory: So what does your mother do?
Girls: (in unison) We don't have a mother.
*cut to Major Glory looking over at Mucho Muchacho and Birdman, all three looking uncomfortable*
To drive it in further, Batman was earlier shown sitting next to Birdman, meaning he would've been just off-screen for this.
The Unintelligible: Grubber of the Gangreen Gang usually speaks only in raspberries. The rest of the gang members understand him just fine though. Subverted in one episode, where Grubber is shown to be quite eloquent when he straightens his posture. He's also an expert voice mimicker.
Unwilling Suspension: In "Equal Fights," as Femme Fatale falls to the ground, Buttercup grabs her foot and carries her off upside down.
"I See A Funny Cartoon In Your Future" has Madame Argentina tying up three voodoo dolls of the Powerpuffs and hanging them from a tree branch, causing the girls themselves to hang in midair over a cliff.
The splash page of comic book story "The Devil's Playground" (Block Party #43) has Him using his powers to booby-trap the kindergarten playground. Several kids are wrapped up in jungle vines from the jungle gym, and three monkeys appear on the monkey bars—the first holding a boy up by his hands, the second giving Mitch a wedgie, and the third using its tail to hang a girl upside down by one foot.
Up to Eleven: In "Bubblevicious" Bubbles takes the battle simulator and Mojo's laser up to eleven. The dial even shows considerable resistance, like it was never meant to go that high.
Villainous Breakdown: Mojo has these occasionally, most notably at the beginning of "The Rowdyruff Boys", when he starts howling and snarling like a real ape over his many defeats.
Mojo Jojo has a particularly huge one at the end of "Forced Kin" when he finally snaps after being repeatedly defeated by the alien force's Villain Sue trait of unrealistically predicting every attack. But the one thing the alien force didn't predict was Mojo going berserk and beating the crap out of it.
Those are nothing compared to the one he has in The Movie. Up until his monkey army rebels against him, Mojo speaks in a very straightforward manner. Once it becomes apparent that the Chemical X-enhanced simians have their own plots for world domination, he flips out, and starts ranting in his trademark redundant speech-style;
"Nooooo! Stop! Cease! Desist! Do not continue with the ramblings, for my ramblings are the ramblings to be obeyed. For I am king, supreme leader, and all-around dictator. Don't you see? all you monkeys are my plan, so your plans are my plans because you are my plan and my plan was to make you! And I plan to rule the planet! Not to have my plans plan to stop me! I am your creator! I am your king! I am Mojo Jojo! Obey ME!"
HIM also has these, normally after the girls defeat his plans with their sisterly love. He goes from his normal, creepy voice to screaming about how they didn't act like they were supposed to. He has an especially noteable one at the end of "Power Noia", when the girls have turned the tables on him and got him completely at their mercy, for the first time actually begging them to let him go.
Villains Out Shopping: Often. When the super villains aren't doing anything overtly villainous, they're treated like any other citizen of the town. Even by the girls themselves!
Very Special Episode: Even though it's not blantantly stated, "Mojo Jonesin" is obviously a drug episode.
Voice Changeling: Grubber uses this ability in the episode "Telephonies" to stir up trouble.
Walk Through The Camera: In the episode "Stray Bullet" in the scene where Mojo is walking very slowly with a confident look on his face.
Wanting Is Better Than Having: One episode had a collector of Powerpuff Girls' merchandise who freaks out and becomes a villain when his collection is complete: there's nothing left for him to collect except the girls themselves.
When Elders Attack: An old lady does this from the roof of an episode to a Godzilla-like monster, who promptly eats her.
Where the hell is Townsville?: Possibly subverted, if the Professor's directions to his college roommate were correct, Townsville fall somewhere in or near Pasadena, CA. Don't mind that there actually exists a City of Townsville.
Who Would Want to Watch Us?: One episode featured a con-artist "director" allegedly making a movie about the girls. The initial broadcast of this episode was suspiciously close to the release of the actual movie.
Window Pain: Not only do things get thrown through windows, but driven. And the girls occasionally fly through them!
Yoko Oh No: invoked The Powerpuff Girls' plan to break up The Beat-alls. "Moko Jono" is the Yoko to Mojo Jojo's John Lennon.
What makes this not necessarily a YMMV, unlike most examples, is that she's literally the Yoko. The entire episode parodies the history and the songs of the Beatles; it's only obvious that the one who divides the Bad Four is a playoff of Yoko Ono.
This may be a subversion today as Paul McCartney had gone on record recently saying that Yoko was not the reason the Beatles split up.