A shapeshifter is a being that can take different forms, depending on its mood. Pookas can do that; they can also be invisible. That's what makes it so unnerving when they "poof" in, because you never know what you're gonna be looking at when they appear. But you know what a dog is like, or a horse, or a rabbit, how can you describe the character of something that can be anything?Tell me all about 'shapeshifters' in 5 sentences or less.