Donny the unicorn returns to Townsville for a student/pony program, much to Bubbles' delight. However, after a first day at school, he makes a new friend named Chelsea, much to the jealousy to Bubbles, which threatens to drive a wedge in their friendship.
When Chelsea open up her face-plates, it references the indie horror game Five Nights At Freddy's: Sister Location, where the characters open THEIR faceplates when they jumpscare the player.
This explains why Chelsea befriends with Donny because it was Mojo, who is planning to make Chelsea luring Donny to his lair in order to use unicorn magic to build his death ray.
It is never explained why Marybelle had a boyfriend, either she was a single parent or divorced.
The title of this episode is a reference of a phrase "odd one out", meaning a person who differs from the other members of the group.
Season 1:Monkey See, Doggie Do • Mommy Fearest • Insect Inside • Powerpuff Bluff • Octi Evil • Geshundfight • Buttercrush • Fuzzy Logic • Boogie Frights • Abracadaver • Telephonies • Tough Love • Major Competition • Mr. Mojo's Rising • Paste Makes Waste • Ice Sore • Bubblevicious • The Bare Facts • Cat Man Do • Impeach Fuzz • Just Another Manic Mojo • Mime for a Change • The Rowdyruff Boys • Uh Oh Dynamo Season 2:Stuck Up, Up and Away • Schoolhouse Rocked • Collect Her • Supper Villain • Birthday Bash • Too Pooped to Puff • Beat Your Greens • Down n' Dirty • Dream Scheme • You Snooze You Lose • Slave the Day • Los Dos Mojos • A Very Special Blossom • Daylight Savings • Mo Job • Pet Feud • Imaginary Fiend • Cootie Gras • The Powerpuff Girls Best Rainy Day Adventure Ever • Just Desserts • Twisted Sister • Cover Up • Speed Demon • Mojo Jonesin • Something's a Ms. • Slumbering with the Enemy Season 3:Fallen Arches • The Mane Event • Town and Out • Child Fearing • Criss Cross Crisis • Bubblevision • Bought and Scold • Gettin' Twiggy With It • Cop Out • Three Girls and a Monster • Monkey See, Doggy Two • Jewel of the Aisle • Super Zeroes • Candy Is Dandy • Catastrophe • Hot Air Buffoon • Ploys R' Us • The Headsucker's Moxy • Equal Fights • Powerprof. • Moral Decay • Meet the Beat Alls • Helter Shelter • Power Lunch Season 4:Film Flam • All Chalked Up • Get Back Jojo • Him Diddle Riddle • Super Friends • Members Only • Nano of the North • Stray Bullet • Forced Kin • Knock It Off Season 5:Keen on Keane • Not So Awesome Blossom • Power-Noia • Monstra-City • Shut the Pup Up • Toast of the Town • Divide and Conquer • Burglar Alarmed • Shotgun Wedding • Save Mojo • Substitute Creature • The Boys Are Back in Town • See Me, Feel Me, Gnomey • Pee Pee G's • Boy Toys • Seed No Evil • The City of Clipsville • Lying Around the House • Bubble Boy • A Documentary • Girls Gone Mild • Curses • Bang for Your Buck • Silent Treatment • Sweet 'n' Sour Season 6:Prime Mates • Coupe D'Etat • Makes Zen to Me • Say Uncle • Reeking Havoc • Live & Let Dynamo • Mo' Linguish • Oops, I Did It Again • A Made Up Story • Little Miss Interprets • Night Mayor • Custody Battle • The City of Nutsville • Aspirations • That's Not My Baby • Simian Says • Sun Scream • The City of Frownsville • West in Pieces • Crazy Mixed Up Puffs • Mizzen in Action • Roughing It Up • What's the Big Idea? • Nuthin' Special • Neighbor Hood • I See a Funny Cartoon in Your Future • Octi-Gone Reboot:
