Project details and more info here.
A realistic unicorn skull, according to the evolutionary biology textbooks I referenced.
This looks fantastic printed in white filament, and even better cleaned up and painted. If you have access to a metal printer (or care to pay for it), I highly recommend that.
I can't take credit for the scan of an actual horse skull, but it required heavy cleanup and editing.
I've included here the entire unicorn skull, as well as the horse skull and unicorn horn as separate files. I've had more luck printing the skull in two parts and bonding post-process.
Use and enjoy!
Adafruit's 3D Printed Unicorn Horn
Marchal Geoffrey's 3D scan of a horse skull via Sketchfab