Princess Butterfly Kiss is Marshmallow's majestic, off-white, pet unicorn. She was first seen at the end of Viral Vote. She was lying down with Marshmallow on top but is only a picture. She appeared in Best Fiends Forever in Marshmallow's photo that was burnt by Grapefruit, causing Marshmallow's rage. She made a reappearance in Nyan Nya Orange.
In Wazzup Blowup, Marshmallow's cell phone background is Princess Butterfly Kiss, as shown here.