When Team Rocket see Ash and Kiawe demonstrating Z-moves, they plot to find Z-crystals for themselves. While searching, Team Rocket run into Team Skull. Both gangs spot a Darkinium Z-crystal embedded in a large rock. The problem is, the rock is the current lair of the Raticate and Rattata infestation from earlier. The two gangs compete to acquire the Z-crystal. Team Rocket emerges the winners, but find out that having the Z-crystal in their possession is one thing, but figuring out how to use it is another. (Source: Wikipedia)
