Balloony was Dr. Heinz Doofenshmirtz's best friend back in Gilmelschtump. He is a balloon with a very well made face drawn on it. He was lost one night when he floated away, Heinz tried to grab him but his father told him to stay still because he was being a lawn gnome.
Balloony was then found years later aboard Mitch's poaching ship as one of the creatures he captured illegally. Mitch had renamed him Colin and called him his best friend. Heinz argues that Balloony was his best friend. Doofenshmirtz tells Balloony to come out of the ship with him, but Balloony didn't budge. This upsets the evil scientist and he says that Balloony has changed. He then realizes that his real best friend is Perry the Platypus. Just as he starts to say this aloud, Agent P climbs into the ship and punches him down the hole in the floor, causing him to fall to his doom. Perry then jumps out after Doofenshmirtz to save his nemesis. ("The Chronicles of Meap")
Balloony was referenced in Robot Rodeo, Doofenshmirtz won the Inator contest, his prize was a small red balloon, He named it Balloony 2