Balloony/Colin is a balloon Doofenshmirtz acquired as a child. He drew a realistic face on it and made it his companion.
Balloony was a balloon obtained at a carnival by Dr. Heinz Doofenshmirtz in his youth in Gimmelshtump. He then drew a face on it, sprayed it with a special lifelong lasting spray, and made it his best friend. Unfortunately for him, he lost it one night during his regular duty of acting as a lawn gnome when it drifted away in the wind.
Many years later, Doofenshmirtz attempted to recover Balloony using the Static Electro Amplif-inator, and although this plan didn't work as he'd hoped, he found Balloony aboard Mitch's poaching ship as one of the creatures in illegal captivity. Mitch had renamed it "Colin" and called it his best friend. Heinz eventually rages at Mitch out of frustration and tries to leave with Balloony, only to be dismayed when the balloon seems to be choosing to stay with Mitch. He begins to demonstrate his anger on Balloony, forgetting the friendship they'd once shared and mentioning Perry the Platypus as his true best friend. He finishes his rant just as Perry himself arrives and punches him, sending him stumbling backwards into the hole in the floor and causing him to fall towards the city below. Perry would jump out the hole to save Doofenshmirtz afterwards ("The Chronicles of Meap")Balloony was later referenced when Doofenshmirtz won the Inator contest. His prize was a small red balloon, which he named Balloony 2 ("Robot Rodeo").
When Doofenshmirtz goes back to Mitch's ship later, he finds Balloony again, but this time wearing a Robo-Suit and wielding weapons, as well as commanding a group of Mitch's robots. Balloony at first tries to defeat Doofenshmirtz, but when Doofenshmirtz (along with Perry the Platypus and Peter the Panda ) is taken down by the robots, he pleads with Balloony, who has a change of heart and defeats the robots, saying the trio (much to Perry and Peter's astounded surprise). Doofenshmirtz is very happy, and begins to tell Balloony about all the good times they can have together again, till Balloony gets hit by a final shot from one of the fallen robots and dies (or pops) to Doofenshmirtz's extreme dismay. Some time later, Perry (feeling sorry for Doofenshmirtz) had brought Balloony newly inflated (with a band-aid) back to him, finally resolving the backstory. Doofenshmirtz and Balloony then have a really good time together making up for all the time they were apart. ("Meapless in Seattle").
While hosting the clip-show about Doofenshmirtz's life, Norm brings up Balloony. Doofenshmirtz was glad to see Balloony but it soon pops. Doofenshmirtz shouts in terror until Norm tells him that it was not the real Balloony and the real one "popped 3 weeks ago" (This Is Your Backstory).
- The face on Balloony is slightly reminiscent of Bing Crosby as depicted in the classic Tex Avery cartoon, Hollywood Steps Out (1941).
- In the Phineas and Ferb: Across the 2nd Dimension video game, he can talk at the Balloon Dimension.
- Balloony is seen in the background of the song Back in Gimmelshtump.
- Balloony got popped in "Meapless in Seattle" but was later fixed by Perry the Platypus, who gave him a band-aid.
- In "Meapless in Seattle", Balloony seems to be alive and mobile. This may be explained by the mechanical suit he was inhabiting, which could possibly contain artificial intelligence as Mitch's does.
- He has made several appearances in "Where's My Perry?", as he is in every Bonus Level.