We are soon shown a mansion where two kids are wandering around with a rag doll that was alive who was actually an imaginary friend known as World.

"Where could Bloo be?" Phoebe wondered.

"Huh... He must've hidden in the house somewhere." Mac shrugged to her.

"Oh... This must be that Foster's place you guys talked about!" Lionel remarked.

"I thought it seemed familiar!" Patch beamed.

"And look, there's Phoebe!" Atticus pointed out.

"Oh, right; Thor's sister." Lionel remembered.

"This must be the place." Blossom said.

Mac, World, and Phoebe soon found Bloo and it was now Mac's turn to count.

"Ten!" Mac said before seeing he had company. "Whoa! Hey! Who are you?"

"We're the Powerpuff Girls!" Blossom smiled.

"We're superheros!" Bubbles added before blushing a bit to Mac.

"We're on a trans-dimensional mission of mega importance!" Buttercup added.

"Not to mention we happen to be needing your help!" Lionel added.

"Cool!" Mac beamed before looking over. "Atticus, Cherry, Mo, and Patch?"

"Man, who HASN'T Cherry met?" Cath asked before smirking as she remembered something from when she met Rocky & Bullwinkle with them. "Oh, yeah, The Cheetah Girls."

Lionel shrugged. "Eh...also, name's Lionel. Pleased to meet'cha! Cherry and Atticus have told me a lot of stuff about ya, but it's all good." he explained.

"Well, that's good." Mac smiled.

"And I'm Cathleen Ross," Cath added. "Cherry's best friend."

"One of them anyway." Patch replied.

Cath growled like a wolf from that to scare him.

"...Is that supposed to scare me?" Patch asked.

"Yeah, cuz I'm part wolf, remember?" Cath replied. "I'm not ordinary and neither are the wolves back at my house."

"Listen, big shot, I've seen crap that would make your fur turn white," replied Patch. "And these wolves are supposed to scare me? Yeah... I don't think so."

"Good to see ya, Mac." Cherry smiled to the boy.

"Good to see you too." Mac smiled back.

"Do you live here?" Buttercup asked the boy.

"Not really, I hang out here a lot though," Mac replied. "This is a home for imaginary friends."

And so Cherry and Atticus explained to the Powerpuffs how Foster's worked and their adventures with Mac.

"It sounds like a lot of fun!" Bubbles gushed.

"It can be at times, Bubs." Cherry replied.

"We're looking for someone," Blossom told Mac. "A big, green monster named Dee Dee."

"Dee Dee? I KNEW Bloo was up to something!" Mac replied.

"You've seen her?" Buttercup glared. "Where is she?"

"I have no idea," Mac shrugged with a small frown. "Hiding somewhere. We just started a game of Ultimate Hide 'n Seek."

"Mind if we help you look?" suggested Lionel. "More eyes are better than two!"

"Did he just call me a-" Cath glared.

"MORE eyes, MORE!" Cherry told her. "Besides, I doubt he'd call you a Four Eyes."

"Yeah! So make yourself useful and put those peepers of yours to work!" Lionel added.

"Come on, we better go inside," Phoebe suggested as she came to the doors with Mac. "Someone's bound to have seen her."

"Yeah! Come on!" Mac added in agreement. "We'll start on the ground floor and work our way up!"

And so they went inside.

Lionel gave an impressed whistle. "Blathering Blatherskite! This place is ginormous!" he exclaimed.

"How many imaginary friends live here?" asked Buttercup.

"Um...a lot." replied Mac. "We'd better start looking. Game's not over until we find everyone."

And so, they began their search.

"There's Wilt!" Phoebe spotted.

"Aw, nuts." Wilt pouted once he was found by the others.

"These are the Powerpuff Girls and Cherry, Atticus, Mo, and Patch's other friends: Cathleen and Lionel," Mac introduced. "They're trying to find that new girl, Dee Dee. Help us look!"

Wilt smiled and soon removed a pillow to show a purple monster hiding there.

"Traitor!" Eduardo glared.

"Looks like a killer." Cath smirked to Eduardo.

"Not really." Cherry told her.

"Yup!" Mo remarked. "From what I've heard, Eduardo LOOKS big and scary, but he's a total softie! But it was to inspire his creator to be brave!"

"Don't tell me; he likes My Little Pony too." Cath replied.

"You know it's not really girly, right?" Cherry said.

"It's not?" Cath asked.

"Do you think I would watch it if it were so girly?" Cherry replied.

"...No, I guess not..." Cath said.

"Watch before you judge, I've made that mistake myself," Cherry told her before going off. "I don't think Coco can be too far away from here."

"Over here!" Blossom smiled once she saw the bird plane imaginary friend.

"Oh..." Lionel took notes. "Imagined by a castaway on an island, found by two scientists!"

"Co-co, cococococo!" Coco replied.

"Also, 'co-co' is all she can say..." noted Lionel.

"Look at all these people! This is gonna take FOREVER!" exclaimed Buttercup. "We need to split up!"

"But Mac is technically the only one who is 'it'!" Wilt replied. "He needs to find everyone for it to count."

"Well, since this is an extreme situation, we can bend the rules a little," Mac suggested. "I grant you all 'It Status'. Now let's split up and find Dee Dee!"

"Right!" Blossom and Cath replied.

"Gotcha!" Atticus said, opening one door only to find a bunch of other imaginary friends. "Whoops... No Dee Dee here."

"There you are, World!" Phoebe smiled, finding her new imaginary friend in the closet.

"Darn!" exclaimed World.

Buttercup and Wilt found a bunch of other friends hiding in the attic, but no Dee Dee there. Coco and Bubbles found a few more hiding under the carpet, but no sign of Dee Dee.

"Hey, that kid just came out of the closet." Cath laughed about her own joke.

World and Phoebe just looked confused at what Cath said as they helped on the search.

Soon...

"No luck!" Blossom pouted.

"Is this everyone?" Buttercup asked Mac.

"Not quite... Bloo is still missing," Mac replied. "Dee Dee must be with him!"

"Are you guys looking for someone?" A voice soon asked before coming to join them.

"Super Power Man!" Atticus beamed to his old imaginary friend.

"Gurglin' gigawatts! Nice to meet'cha!" Lionel exclaimed, shaking his hand. "We happen to be looking for Bloo, since he's been hiding all day! You seen him?"

"Bloo, huh?" Super Power Man replied. "I think I saw him upstairs somewhere with this new friend in the house."

"Thanks, SPM!" Lionel replied. "Going up!"

"No problem." Super Power Man smiled to them.

"Another perfectly miserable day... But I may as well look my best," A voice said from behind one bedroom door. "Oh, fantastic... Aaaaugh!" The voice then screamed.

"I think I found them." Patch sighed, recognizing the voice.

"Who is that, Natasha Fatale?" Cath scoffed from the voice.

"Nope...worse," remarked Lionel. "YOIKS! Looks like sumthin' a Picasso painting spat up!"

"Duchess." Cherry and Atticus sighed.

"The jig is up!" Bloo cried out as he ran with his new friend. "Come on, Dee Dee, let's make a break for it!"

"Those scoundrels!" Duchess glared and pointed out to the others. "They went that way!"

"Come on!" Mac told the others.

"But first, let's put on a song for the Scooby-Doo chase scene." Cath said as she took out a random record.

"This is a fan fiction! Nobody's gonna be able to hear it!" Lionel replied.

"But it's a running joke." Cath pouted.

"Yeah, about your running jokes..." Cherry said, a bit uneasily.

"Come on, let's go!" Phoebe piped up, taking Cherry by her hand to run with her. "We gotta get that Dee Dee girl, Miss Cherry!"

"Aw, don't call me 'Miss', that makes me feel old." Cherry replied.

"Besides, this should be over quick, so there won't be any time for a chase scene soundtrack anyway!" Lionel added as they took off after Bloo and Dee Dee.

"I really love hanging out here." Phoebe smiled.

"I thought you might like it." World smiled back to her.

"Bloo, stop!" Mac called out.

"NEVER!" Bloo called back.

The both of them took a left into Mr. Herriman's office.

"Master Blooregard, what is the meaning of this?!" exclaimed Mr. Herriman.

"Mr. Herriman, I'll explain later!" replied Bloo. "Hide us!"

But at that point, Mac and the others had come in. "Found ya, Bloo!" said Mac. "It's OVER!"

"Give up, Bloo! There's nowhere left to run!" Phoebe added.

"You'll have to tag us first!" Bloo glared, backing up against the wall with Dee Dee.

"Please! Dee Dee is our friend!" Blossom told him. "She is mutated and bouncing through universes! We need to bring her back home to help her!"

Bloo looked wide-eyed to Dee Dee. "'Zat true?"

Suddenly, Dee Dee hiccuped, zapping away yet again.

"Oh, come on!" Atticus complained.

"Wow... She's really good at hide and seek..." Bloo replied.

"Oh, no!" groaned Patch.

"Here we go again!" sighed Lionel.

"Doing this all the time over and over is starting to bug me!" Cath complained. "Can't we just bring Dee Dee back here by, oh, I dunno, magic?"

"No." Cherry said.

"Why not?" Cath asked.

"If we solved EVERY SINGLE task with magic, there wouldn't be much of a story, now would it?" Cherry replied.

"Yeah! Plus, we'd never learn to do anything under our own power!" Lionel added. "Magic can only guide you a little of the way, but you can't rely on it to solve every problem!"

"We better go back to Dexter now." Cherry said.

"Who's Dexter? Who's Dexter?" Phoebe smirked, jumping on her back.

"Friend of ours." Cherry replied.

"And knowing him, he won't be too happy about this!" Lionel sighed. "So you better keep that world-renowned temper of yours under control, Cath!"

Cath just firmly pouted with her arms crossed.

"Okay, Phoebe, we gotta go," Cherry told the young witchling, taking her off of her back. "We'll see you later."

"Can I tell Thor I saw you guys?" Phoebe asked.

"Sure! ...As long as he doesn't get jealous." Cherry replied.

"Who the heck is Thor?" Cath then asked.

"He's Drell's nephew," explained Lionel. "He's a good guy, but he's a little dim: think Season 1 Patrick, before he became a complete doofus."

"Oh. Okay." Cath said.

"See ya, Bebe," Atticus smiled to the girl. "Thanks for helping us."

"Sure thing." Phoebe smiled back.

And in a crackling flash, they were back in Professor Utonium's laboratory.