Yin! Yang! Yo! Season 2 Episode 39 Yin, Yang Who? Episode Title: Yin, Yang Who? Episode Description: Yin, Yang Who?: In the series finale, Eradicus makes his move to destroy the town after draining Yo's Woo Foo aura. Then he goes after Yin's. Both Yin and Yang embark on a quest to find their parents and retrieve a Woo Foo aura donation, which is the only way to save Yin. The twins discover that Master Yo is actually their biological father, who had his memory of this erased so he could train them "without bias and fear." After learning that Yo is their dad, Yin asks, "If [Master Yo is] our father, then who the heck is our mother?" But even after this, it's never revealed who Yin and Yang's biological mother is.