Theory World 4: Yin and Yang

Theory World 4: Yin and Yang (JP: Theory Story 4: Black Yin and White Yang) is the fourth game in the Theory World series. It is subject to release Summer 2015.

Plot
Twin Australian ghosts Curt and Danielle have vowed to kidnap the innocent residents of Supernannya into their Blood Castle and protect the Platinum Boomerang from the heroes. Soon, they summon their ferocious minions called the Zombie Emus and the Mutant Koalas to invade the world and massacre everything they see.

Can your silent character and the team stop the dreaded duo of dipsticks? ==Differences between Yin and Yang
 * In Yin, Danielle is the dominant of the twins (as females are associated with Yin), whereas in Yang, it's Curt (as males are associated with Yang).
 * In Yin, you must fight a 100-unit team of Zombie Emus before the final bosses. Though in Yang, you fight a 100-unit team of Mutant Koalas instead.