Somewhere over the rainbow you will find our delicious rainbow icing cupcakes! 

Why not add a unicorn horn!?

Unicorn- "a mythical animal typically represented as a horse with a single straight horn projecting from its forehead."

"Something that is highly desirable but difficult to find or obtain."

But is it? REALLY?
.
We don't think so. Not in cupcake terms anyway...
Why don't you find out for yourself?