Candace's Id, also known as Candace's Dark Self, is the main antagonist in the Phineas & Ferb episode; Monster from the Id. She is a "creature" that lives inside Candace Flynn's mind. She also represents Candace's dark side and her urge to bust her brothers.
While Phineas, Ferb, Baljeet, Candace, Isabella, the Fireside girls, and Buford were inside Candace's mind to find a memory, they eventually came across her Id. As soon as the Id encountered them, she began to attack and chase them. Phineas explained that someone has to wake up and shut down the machine to save themselves. They managed to wake Baljeet up by using contractions. Baljeet tried pull the plug, but was unable due to his weak strength. While this was going on, the Id began to devour the ground beneath them, which resulted in the children being dragged into the Id's mouth. However, before they could get eaten, the woke up due to the sheer shock of them being eaten. All except for Buford managed to escape Candace's memory. Buford decided to stay and hang out with Candace's Id.
- Candace's Id wields a Ducky Momo as a Blunt object.