Pikachutwo was a cloned version of Ash's Pikachu. It looks like Ash's Pikachu but has longer shadow like dark black fur patterns on his ears.
Ash's Pikachu was also cloned. The new Pikachu clone became known as Pikachutwo. Pikachutwo resembled Ash's Pikachu in appearence but was much more aggressive and kept attacking his counterpart. Pikachutwo savagely battled Ash's Pikachu to the point of exhaustion. However, Ash's Pikachu refused to fight back, despite Pikachutwo's insistence and attempts to hurt him even when Pikachutwo could only stand when being supported. He was last seen at the end of the movie, flying away with Mewtwo.
Mewtwo with the cloned Pokemon head for Johto and arrive at Mount Quena. Pikachutwo thinks he and the cloned Pokemon have a right to live in the world although they are just clones. Pikachutwo would eventually help Ash and his friends protect Mewtwo from Team Rocket, although Ash and his Pikachu had their memories about Mewtwo in the past erased.