Classification: The Dark Pokémon
Description: Yin-Xing is the opposite of Yang-Xing in every way. It is said to embody everything that is dark in the world.
Evolves into Yin-Yang-Xing by leveling up with a Yang-Xing on the team
Trivia: In order to maintain its purity of darkness, Yin-Xing expels any and all light from its body into its white gems. Although it is the polar opposite of Yang-Xing, the two will get together well. It is not complete until it merges with a Yang-Xing that it has grown in synch with.
Classification: The Balance Pokémon
Description: Upon reaching maturity, a pair of Yin-Xing and Yang-Xing will merge together to form this Pokémon. It said represent balance and unity.
Evolves from Yin-Xing and Yang-Xing fusing together
Trivia: Having merged from two Pokémon, one of pure light and the other of pure darkness, Yin-Yang-Xing has achieved a state of perfect balance. It is calm of mind, and always considers both sides of any issue. The minds of Yin-Xing and Yang-Xing no longer exist as separate entities, and instead work together as one mind combing the experiences and knowledge of the two.
How Does “Fusion” Evolution Work? Mechanically speaking, both Yin-Xing and Yang-Xing exolve into Yin-Yang-Xing by fulfilling the requirement of leveling them up while the other is on the team. The one that levels up first is the one that evolves, meaning that its nickname, level, moves, EVs, IVs, gender, nature, and other values are kept upon evolution, while the one that didn’t level up is “consumed” by the evolution and disappears from the party, having merged with the other. The second one’s values are not kept or considered in this evolution.