Sick of Stephanie constantly interfering with his plans to defeat Sportacus, Robbie makes an evil windup double of her to say mean things to everyone and make the real Stephanie leave, furthered by claiming the real Stephanie is the imposter. The only way to tell who's who is with a dance contest—but can Stephanie win?
This episode contains examples of:
- Chekhov's Skill: Subverted—early in the episode, Stephanie is demonstrating her latest dance moves to her friends, including a new jump that she's perfected. Robo-Stephanie later uses this move during the dance-off, but the real Stephanie doesn't as part of her plan to expose the impostor.
- Dance-Off: The adults decide that since Stephanie loves dancing, the only way to determine which of the two Stephanies is real and which is a duplicate is with a dance contest.
- A Day in the Limelight: This is a rare Trixie-centric episode, with a special focus on her and Stephanie's close friendship.
- Evil Twin: Robbie makes an evil clone of Stephanie to confuse everyone.
- Judgment of Solomon: Stephanie's plan to prove herself the "good" twin uses this at its heart. During the big dance-off between the Stephanies, Robo-Stephanie ends her routine with a flashy jump move that the real Stephanie had been practicing earlier. The real Stephanie doesn't do this jump, and all of the adults figure that the robot must be the real deal because she's the better dancer. Trixie, however, determines that the Stephanie who didn't jump is the real one—she could have easily performed the move, but chose not to because she believed in her friends and their ability to know the truth.
- Make My Monster Grow: Robo-Stephanie is originally just a toy figurine. Robbie uses a machine to make it grow to the size of the real Stephanie.
- Near-Villain Victory: Robbie comes surprisingly close to succeeding in his plan to have Stephanie kicked out of Lazytown. His robot duplicate is declared the winner of the dance-off, and if it weren't for Trixie figuring out the real Stephanie's plan, the adults would have fallen for the fake and exiled the real one.
- Paint It Black: The fake Stephanie has black beads in her headband, while the real Stephanie has white beads.
- The Power of Friendship: Stephanie relies on this trope to prove her true identity to the people of Lazytown. She trusts that their friendship with her will be enough for them to know that she's the genuine Stephanie.
- Pragmatic Villainy: Robbie realizes that his schemes to destroy Sportacus often fail because of Stephanie, and so decides to go after her instead. Furthermore, rather than taking her on in a physical confrontation, he has Robo-Stephanie act horrifically mean to everyone in town, turning the citizens against her.
- Secret Message Wink: This is how the real Stephanie relays her identity to Trixie after the dance-off.
- "Shaggy Dog" Story: The question of which Stephanie is real is ultimately solved when, after the dance-off, Robo-Stephanie reverts to her original toy form. Downplayed in that Trixie's figuring out the actual Stephanie's identity and her subsequent impassioned speech keeps the adults from exiling her long enough for the duplicate to change back, although Trixie didn't know that would happen.
- Spot the Imposter: It's right there in the title: "Who's Who?"
- Too Dumb to Live: Somehow, the citizens of Lazytown don't realize that one of the two Stephanies is a horrible bully to everyone, while the real Stephanie has been nothing but kind and sweet since the instant she arrived.
- Two Girls to a Team: The episode focuses on Trixie and Stephanie being best friends because they are the only two girls in the main group.
- Unspoken Plan Guarantee: Exaggerated regarding the Judgment of Solomon described above. Stephanie doesn't tell anyone about her plan to expose the impostor and simply puts it into action. Her only way of communicating that she's up to something is the Secret Message Wink she throws to Trixie, who thankfully figures out what she's doing and tells the adults.
- What Measure Is a Non-Human?: It's unclear just how much free will Robo-Stephanie actually had, but once she's turned back into a toy at the end of the episode, no one's concerned for her in the slightest.
