Designed in a laboratory to be an organic weapon in imitation of MB, she escaped into the world because of her creators' continuing ill intentions. Yinyang represents ultimate balance. (Her designer, 'Shadow' was who came up with this specific design.)
Yinyang is a heavy working off of MB, which was used as a base.
There is only a final stage model, done in Maya 8. She has three primary color maps of 2048x2048 and 1024x1024 sizes, with many texture maps of varying scales for reflectivity, glows, et cetera. The final model is 110869 tris and equipped with half a dozen expressions. They are intended for varying media.