My niece is wanting a Monster High cake. I bought a square cookie cutter and squished the sides in some so that it is a diamond. But, I am not sure how to do this with 3 colors. Should I cover the entire cake in purple, then cut out diamonds of black and pink? If anyone can help it would be great!

You can do a monster high search on here and there's a lot of photos that'll help give you ideas.

When I made mine, I covered the cake in black and then cut diamonds to put over it in black, purple and white. The pattern doesn't work on the top of the cake because of the shape of the diamonds.