I call them shapeshifters.
Its a really fun idea - First draw a random shape. It doesnt matter how it looks like, as long as there are no wholes in the line.
Second: Start drawing inside the shape and try to make SOMETHING out of it. A creature, a human, it doesnt matter, but creatures are especially fun to do.
We had a hell of fun doing this and it doesnt matter how they look, everyone can do those.
So grap some friends, some pens, paper and a beer and go for it. ^^
The last scan is just a page from my mini sketchbook by the way.