I cosplayed as Unikitty at an event that was showing The Lego Movie. I made the mask myself by taping two cereal boxes together for the head, cutting two corners from breakfast bar boxes for the ears, using a colored paper towel roll for the horn as well as using a toilet paper roll, a cardboard flap, and masking tape for the bottom part, covering the box parts with felt, and making the face. I do have a tail as well (made out of pipecleaners) but you can't see it.
I was inspired by this person's Unikitty costume in this picture www.deviantart.com/art/MCM-Exp…
Picture is (c)
Unikitty is (c) Phil Lord, Christopher Miller, and Warner Bros.