In The Simpsons episode "The Dad Who Knew Too Little", Homer and Lisa are framed for a crime and go on the run. They use a black hair gel to disguise themselves, and Lisa comments that she looks like a Powerpuff Girl, complete with Buttercup's hairline◊.
Mac is based on a one-time character, Mike Believe, who had a mischievous imaginary friend of his own.
In the pilot episode, Mojo Jojo note Or rather an imaginary friend clone, created by a kid who just copied what he or she saw on television appears as one of the imaginary friends Wilt introduces Mac and Bloo to.
Frankie's T-shirt has silhouettes of Blossom, Bubbles, and Buttercup on it, each color corresponding with their eyes and dress.
In the episode, "Land of the Flea", one of the fleas living on Eduardo resembles and sounds like The Mayor. It doubles as an Actor Allusion, since Tom Kenny voiced both The Mayor and Eduardo.
In the episode, "Say It Isn't Sew", when Bloo looks through some stickers, one of them is of Blossom's head.
In the episode, "Nightmare on Wilson Way", Oscar (The big green friend) decides to go Trick or Treating as Blossom, only to find out that Frankie has decided to go Trick or Treating as Blossom as well, which leads to him walking away muttering, "I should have gone as Bubbles...". In all later scenes he appears in, he's dressed as Bubbles. Also in the same episode, Bloo is dressed as Mojo Jojo in a flashback.
In the episode, "Challenge of the Superfriends", Mac and Bloo meet a superhero imaginary friend named Imaginary Man who looks like a cross between Major Man and Major Glory from Dexter's Laboratory. The episode in general has many references to the series, as it begins with a narrator saying "The City" the way he would at the beginning of each episode, and ends with Bloo saying, "And so once again the day is saved". Also, whenever Imaginary Man and his enemy sister Nemisisister flew, they would make the same sounds and leave behind streaks of light the way the Powerpuff Girls do.
At the end of the The Grim Adventures of Billy & Mandy episode, "My Fair Mandy", Mandy smiling for the first time messes with the natural order and sends her, Grim, and Billy to the Powerpuff Girls' dimension. Grim is dressed as Blossom, Mandy is dressed as Bubbles, and Billy is dressed as Buttercup, and Professor Utonium tells them that Mojo Jojo snuck into a movie theater without paying. In The Stinger, Irwin is seen in Mojo's evil lair, dressed as Mojo himself.