I remember a few mistakes I made regarding The Muppet Christmas Carol, before I saw the movie, so this was based on the trailers. First, there's one scene that was in many commercials where Miss Piggy says "whatever!", her voice sounded a bit deeper and more man-like. I noticed that and thought that Miss Piggy would be put under some sort of spell making her evil and sound like a man. This was before I knew that Miss Piggy WAS performed by a man (I think I knew by then that the Muppets were puppets).
I also thought that Belinda and Betina were supposed to be bad girls, if not evil. One reason was due to them being with Miss Piggy in that one scene mentioned above, but also because the commercials showed that scene where they run up to Kermit and push him into the door, out of love and excitement that daddy is home. But when I saw that scene, I thought that them pushing Kermit to the door was out of some evil motive.