I like the "Dinos in space" and "Frankenstein" idea. The latter would require at least six participants to create a head, a body, right arm, left arm, right leg, left leg. Or everyone designs a complete figure with interchanging limbs to mix and match.
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Well, we did "Tops and Tails" which is a simplified version of that. (https://itch.io/jam/paper-jam-003)