If you’ve seen Cabin in the Woods, you’ll never look at Unicorns the same way again. 
Or Mermen!
Also, the hell with lamprey faced ballerinas…urghh :eek: I had a nightmare one was riding on a unicorn and I was begging her to please just…turn around. She shook her lamprey faced head defiantly.
There’s a series of books by Diana Peterfreund (I’ve only read the first, but it wasn’t bad) about unicorn slayers. (The unicorns are dangerous monsters.) The first book is Rampant.
In P.C. Hodgell’s Godstalk Chronicles, the local unicorns in Rathillien are called “rathorns”. They’re heavily armored predators, their battle cry induces panic, and they can project their emotions in some fashion (apparently a combination of psychic projection and pheromones). A rathorn in a bad mood can wither vegetation just by standing there, being pissed off or depressed…which are not uncommon states for a rathorn to be in. Oh, and they’re at least semi-intelligent, and inclined to be vengeful.
The heroine wants to ride one, of course.
The best guess of me and the Internet is that she is the “Sugarplum Fairy” mentioned on the betting white board.
Now have visions of sugarplums dance through your head…
I remember an evil unicorns/good dragons book from childhood. Peterfreund is too recent.