During the final fight a henchman tumbles down the stairs of the saucer to the floor then after a cut the floor is clear and the henchman tumbles down again.
The contours of the saucer in flight look nothing like it when on the ground.
During the ride in his flying saucer, Joker says that Saturn is "just a few billion miles away." In actuality, Saturn averages a distance of 886 million miles away from Earth.
During the fight at the end, and everyone is inside the saucer, you can see the henchmen standing near the entrance, waiting for their cues to go tumbling out without being hit. You can also see Adam West standing in the background on the left and doing absolutely nothing.
The stock footage that shows the Batmobile leaving the Batcave very quickly only has Batman in the vehicle. Robin is not in the passenger seat. This is most likely the same footage in many episodes.
When joker landed his saucer, Alfred hit his head on the top exit door when exiting the saucer.
It is not clear how Joker's black henchman "Shamrock" is knocked unconscious during the final fight scene. He is briefly seen slumped in a chair. Neither Batman nor Robin are ever seen hitting him or even being within 5 yards near him.