So, the top tier of my cake is a 6" cake. I was wanting to put a Minnie Mouse hat on the top of it using 1/2 of my ball pan but that is about 6" so it won't look right. I was thinking I could make it and just carve it smaller, but I'm worried it won't look right since I've never carved anything. My other idea was to make up a big cake ball (like for cake pops) and cut the bottom off to make it look like the bottom of a hat. For those of you who have made cake balls before, would it work if I put the cake ball in the freezer to make it hard, then cover it in black fondant? Or should I dip it in chocolate? This cake is due tomorrow so quick help is appreciated! Thanks!

You can use a small glass oven safe bowl if you have one. Still might require a little carving but not much.

I have used cake ball dough for my cakes. If you see my photos, I have used it in the dogs heads (both box and bag), and I have used it in the fairy body and head (the one with wings)
For it, I did a hard dough. I added crushed biscuits to it, and it was very easy to use. I covered everything with mmf.
I am most sure you can use cake ball for what you are saying.

Thanks!