Goofs

The gum Miss Piggy inadvertently gets her hand stuck to just before getting her purse snatched was clearly not there when she first came up to the lamppost.

Dr. Teeth and the Electric Mayhem are on stage for the wedding while still playing in the orchestra.

In the "Muppet Babies" dream sequence, the first time Kermit rides by on the tricycle the string pulling him is briefly visible.

When Kermit is hit by a car, the close-up of the car coming to camera is reversed. To the right of the frame, the people on the sidewalk are walking backward and sped up, indicating that the shot was done with the cab going in reverse at a fast frame rate and later was reversed printed.

When Miss Piggy karate chops Kermit into a chair and he finally snaps out of his amnesia, he hits the chair upside down. This would've required Kermit to turn 180 degrees still facing everybody as he's flying towards it, which would be impossible due to the laws of physics.

The rats all come up a lot higher off the ground than they should.

When Kermit plays "All Together Again" with the glasses of water, the cups with more water produce a higher sound. In reality, it's the opposite.

Miss Piggy's train makes noises like it is being pulled by a steam locomotive, but it is self-propelled electrically-powered cars.

When Kermit says "Yes" in Martin Price's office after Fozzie tells him that Price/Plotsky only wanted their money, his mouth doesn't move.

At the end of the Muppet Babies number, when Miss Piggy tumbles down the slide onto Kermit, she sings the final high note while clearly sucking on her hand.

In the opening sequence, you can see Frank Oz's head below a dancing Miss Piggy.

In several of the shots at Sardi's of the disguised Kermit The Frog when he is sitting behind the table, Henson's hair is visible just above the table on the right.

Kermit should have known Miss Piggy wasn't going far - the train she leaves on is the Erie Lackawanna Railroad which was a local railroad servicing only New Jersey. Erie Lackawanna shut down in 1983 when it was taken over by New Jersey Transit Corporation.