I learned this from Omi Yusuke and Tada Keisuke, students in a course I teach at Meiji University, in Tokyo. I like the way the gradual addition of features, and the inclusion of non-human elements, leads to an "exquisite corpse"-like creature. The addition of a complete object at the end creates an interesting contrast with the piecemeal creature. The creature's uniqueness makes it an interesting object for description and imaginative writing.
Participants pair-up or form groups of no more than four.