Robot Bulls
The robot bulls were one of Phineasand Ferb's Big Ideas.
The robot bulls were created by Phineas and Ferb for the robot rodeo that they made because Isabella needed a Rodeo Clown Patch. During the rodeo, Heinz turned his fog machine on, fogging up Danville and turning it into a rodeo with fog, the problems start when Buford says that a red-balloon is making the bulls angry, when a kid let it go, the bulls knock off the riders and go after the balloon, taking the rodeo as they go after it ("Robot Rodeo").
The Robot Bulls were re-built by the O.W.C.A. for stopping the Normbots with other Big Ideas, allowing Phineas and Ferb to save the Tri-State Area of Dr. Doofenshmirtz-2. (Phineas and Ferb the Movie: Across the 2nd Dimension).