Art by Bittergrey, thanks to him for going with my idea. http://www.furaffinity.net/view/29219037 Here is what he says about it :

An idea from loupylupine loupylupine prompted by the shortage of unicorns. http://www.furaffinity.net/view/26022775/

The staging on this one was difficult. To show that it was a narwhal costume, it was necessary to show the tailfins and horn. To show that it was supposed to be a unicorn costume, the box was necessary. However, I also wanted to show Loupy reacting to it. The result was to have it mostly folded up in the box, with horn and tail showing.

Coloring it would bring another complication. A blue color would make it more clearly a narwhal costume. Aquatic blue would also be unisex... but there was a temptation to try to make it princess pink instead.