My black cat costume was simply awesome. It consisted of a set of home made cat ears attached to a black fuzzy cloth made out of the same material that stretched over the top of my head and was fastened by little shiny black ribbons under my chin. The body was a solid black long sleeved dance leotard with a bushy black tail in the same material as the head piece attached at the back. I wore black tights and black shiny Alice-in-Wonderland shoes (also known as Mary Jane shoes). It was complicated enough that I needed help getting it on and the makeup put on my face was itchy, but my mom made sure to tell me not to touch it when it itches, because it would get ruined.
It wasn't originally a Halloween costume, but was made for the Kindergarten program. I played the black cat in the program, and I think it had something to do with the black cat song. I don't remember a lot about what it was about, but I specifically remember weaving through what was supposed to be trees while the kids were singing about the black cat. I know there are a couple of black cat children's songs, and I don't remember which one it was.
I was totally a cat lover as a child (dogs scared me in general--an exception being my aunt's dog Ellie, particularly when they barked), so that was a no-brainer on why I loved this costume so much. I think I wore it two years in a row, but then it got worn out, and I outgrew it. Nothing after that was quite as much fun, and I was an awesome black cat. Just saying. Unfortunately, no photos exist of this costume.
I've looked up to see what kind of children's songs about black cats there are, and this one resembles my memory the most. It may not be the actual song, since I don't know the tune's age (it's clearly modernized here), but it should give you enough of an idea to imagine the little five-year-old tow-headed girl pretending to be a black cat wandering on a school auditorium stage.