Elisabeth "Sissy" Blakley is Johnny's on/off romantic antagonist.
Sissy is a 12 year-old girl who's a rival of Johnny who's younger than her, and she is much smarter than him. In the show, she likes (also love) Johnny and Johnny also seems to have a crush on her, but he doesn't hide it as well as her, although he doesn't show it because he mocks her and makes fun of her (e.g., when Johnny refused Dukey's claim that he actually likes Sissy by announcing that he hates Sissy, Dukey told him, "At your age, Johnny, it's the same thing"). However, the two are constantly competing against each other. If Sissy beats him, she will brag about it. If Johnny wins, he'll either get caught into a situation because of it, or brag as much as her.
In "Saturday Night's Alright for Johnny", Johnny pretends to get used to being bullied by Sissy and they fall in love with each other along with Dukey and Missy. She seems to be the victim to the show's twists, adventures, and misadventures at the end of the episodes that she appears in. She appears in the first and second season but made a brief cameo in the background during an episode in Season Three, and several appearances in season 4 with a few in seasons 5 and 6. Sissy may actually like Johnny, because in Princess Johnny, she was paying him to play princess with her, and in The Good, the Bad & the Johnny, after Johnny gives flowers to her, she kisses him, and in Johnny Irresistible it shows that Sissy likes him because she says "I wanna kiss him, and kiss him, and kiss him!" She also appears to like him in Johnny B.C because Sissy "in love" is a sign Susan and Dukey use to find Johnny after Johnny (who was still a caveman) licks Sissy. But her love for Johnny was obvious in IJohnny episode, where she found Johnny's clone and date with it.
Sissy has waist long blonde hair held back in a pony tail with bangs curled up and a red lightning bolt shaped streak covered by a red plaid head band. She has multiple ear piercings, has fair skin and large blue eyes with extremely long black eyelashes, a black choker and pink lipstick. Her normal attire consists of a black t-shirt with a blue camisole under with a red plaid skirt over jeans with two crisscrossed white belts and black and white checker board print sneakers. Her eyebrows are very thin and maybe drawn on.
She has worn a ladybird scout uniform consisting of a green skirt, a green polo shirt with a pink bolo tie, a green beret dress with a pink upside down triangle with an acorn in the middle. She also sports a badge sash across that has a large amount of badges on it.
In Johnny Dodgeball, Sissy, being a pro dodge ball player, has a standard uniform consisting of a yellow shirt and shorts with red outlines along with gray sneakers.
When Johnny and Dukey get shrunk down to more then microscopic size and are sent to a alternate universe, the Sissy there appears the same but has red hair and the lightning bolt is blond.
Johnny is the only one she likes in the series and Johnny sort of kind of likes her too. In almost every episode where Sissy appears it has been hinted that she likes him (ex.Saturday Night's Alright for Johnny, and Johnny's 100th Episode). Sissy tends to hide her crush very well through bullying him and asserting superiority over him.
Missy is Sissy's pet and constant companion. Dukey is seen to like her too.
- Johnny Impossible (First appearance)
- Johnny's Extreme Game Controller
- Johnny Dodgeball
- Hoist the Johnny Roger
- Johnny vs. Bling-Bling 2
- Saturday Night's Alright for Johnny
- Johnny Zombie Tea Party
- Johnny vs. Super Soaking Cyborgs
- The Good, the Bad, and the Johnny
- Join the Johnny Scouts
- Johnny B.C.
- Who's Johnny?
- Princess Johnny
- Johnny's New BFF
- Johnny Re-Animated
- Johnny Tube
- Good Ol' Johnny Test
- Spotless Johnny
- Johnny Irresistible
- Johnny's Ultimate Treehouse
- A Holly Johnny Christmas (Cameo appearance)
- Johnny's World Record
- Magic Johnny
- Green Johnny
- Stop in the Name of Johnny
- Johnny's 100th Episode
- Johnny's Next Episode
- Johnny's Supreme Theme
- The Sands of Johnny
- The Johnny Who Saved Halloween
- Future Johnny (Last appearance)
- "You didn't write a play about garbage, Test. THIS IS GARBAGE!" - Good Ol' Johnny Test
- "We DIE?!" - Good Ol' Johnny Test
- "Hey, I'm paying you, remember???" - Princess Johnny
- "I'm William, and I'm TELLING you...you're the apple." - Saturday Night's Alright for Johnny
- "How can you not love a show about a kid who's older brothers do experiments on him?"- Johnny Re-Animated
- "Does that mean you like me?!" - Johnny B.C
- "That's it! I want you out of my life, Johnny Test! So I'll take the F, just so you can go to Crabapple's class, and be gone forever!" - Who's Johnny?
- "Thanks Test, your good!" - The Good, the Bad & the Johnny.
- "I always thought he was kind of cute. Don't tell him I said that!" - Johnny's 100th Episode.
- She is known as the Speedster in school.
- Janet Nelson Junior was intended to take the role of Sissy, but was phased out and was replaced with Sissy for unknown reasons.
- Her name might be a pun on the fact that Johnny thinks girls are sissies.
- Sissy is the first girl to kiss Johnny.
- She first appeared in Johnny Impossible.
- Her only appearance in Season 3 was in Johnnyitis.
- Sissy was in 5th grade in season 1 (2005-2006).
- Sissy's in 6th grade in seasons 2-present (2006-present)