The Cave of Mirrors!

Traversing through Reflection Cave, Ash & co. are checking out the marvels of the cave's reflective structure when Pikachu is taken from Ash by a strange version of Ash. Ash instinctively follows his doppelganger and ends up in a mirror world, where Serena is determined, Clemont is athletic and Bonnie is very "lady-like", all the opposite of the friends he knows. Will Ash be able to find Pikachu and return to his world?