Visible crew/equipment: In the scene when Kermit confronts Doc Hopper he comes walking out of the bar. If you look at the top of Kermit's legs when he walks out, two pair of hands can be seen moving the legs.
Other mistake: Whenever Fozzie is driving the Studebaker, the movements of the car don't correspond to the way he moves the steering wheel (he tends to crank it back and forth a lot).
Continuity mistake: When Gonzo is flying in the air holding on the balloons and then is shot down by Doc Hooper and lands on the car, the last two balloons are yellow and pink, but when the car takes off after Gonzo lands on the roof - the two balloons are now both blue.
Continuity mistake: Kermit's ice cream in the fair scene changes colour.
Visible crew/equipment: In the scene where Kermit meets Fozzie, when Fozzie tosses the rubber chicken over his shoulder you can see Frank Oz's arm and where the glove ends.
Continuity mistake: In the scene where Kermit, Fozzie, and the gang are following Gonzo, who is floating from the helium balloons, Fozzie opens his door and looks up at Gonzo. When he comes back into the car after Kermit shouts at him to do so, the steering wheel comes loose from the dash and all the Muppets start yelling at him for being reckless. In the next shot of the interior, the steering wheel is back in place. I do feel maybe this was a blunder that was left in on purpose, because it was so funny the way all the puppeteers ad-libbed a reaction to what shouldn't have happened, but it fails in continuity because in the next shot the wheel is fine.
Visible crew/equipment: When Kermit and Fozzie are driving to Hollywood, the reflection of the camera and the cameraman's hand are seen in the mirror.
Visible crew/equipment: When the Electric Mayhem Band has finished painting Kermit and Fozzie's car, you see the newly painted car and the band walks into the shot, you can see the head and hand of the puppeteer who is operating Scooter.
Continuity mistake: When Kermit and Fozzie come round the corner and see the billboard with Kermit's face on it, you can see that there is nothing behind the billboard. Yet later when Doc Hopper and Max are leaving, Hopper's car is behind the billboard. The car slightly sticks out, so Kermit and Fozzie should have seen it.
Visible crew/equipment: When Kermit is on his bike and enters the site of the Doc Hopper's Frog Legs Restaurant, look closely at the bike. You can see the wires moving the pedals of the bike; attached to the handlebars and behind the seat. Try to look for it when he rides by the black truck.
Revealing mistake: When Sweetums scares the girls out of the tent, watch the first girl that runs out screaming. If you look at her face closely, you can see that she is smiling.
Other mistake: In the fight scene right after Miss Piggy blasts the man through the wall, she kicks another man. If you look closely, he goes back from the kick a little, then just stands there and adjusts his hat.
Revealing mistake: When Fozzie comes out on stage and starts his act, you can see lines around him, suggesting he was matted into the scene. He also reacts a second too late to the gun being shot by him, and he doesn't cast a shadow.
Audio problem: Fozzie and Kermit are driving right towards Gonzo and Camillia. When Fozzie says, "Yeah, cute huh?" if you look in the mirror, his mouth doesn't move.
Audio problem: When Doc Hopper drives up to the town and some of the muppets are in the bus, Fozzie says "oh no" but it is Scooter's mouth that moves.
Audio problem: When Gonzo is flying over the countryside with the balloons, his mouth never moves during all his lines except "Ah this is the place to be. Whoopeeeeee!"
Plot hole: How did Professor Krassman get shocked into being a frog? The electronic device doesn't even touch his head.
Visible crew/equipment: As Miss Piggy jumps from the overhead platform onto the goons, the man that tossed her is briefly visible as he ducks down.
Revealing mistake: As Kermit walks by the bus, the lower portion of fabric covering the operator's arm is visible.
Revealing mistake: As the camera pans down to Kermit sitting in the empty sound stage, it's easy to tell that the sides of the stool are actually solid with the background painted on them to hide the puppeteer.
Answer: The closest thing to an answer is here, Martin Becker's obituary. His family states that it was a robotic Kermit on a bicycle. Outside of that, everyone else associated with the movie has been quiet on the subject.http://www.fridaythe13thfilms.com/saga/part5/martinbecker.html.
Rlvlk
They used gyros in the wheels - Martin Becker made the first self-driving bike for that movie-now the same tech is used in the self-driving bikes seen in the Netherlands. -Diana Becker, Martin's widow.