Transform is the signature move of Ditto's, with Mew being able to perform it also. It's a special move that allows the user to transform its appearance into that of the opponent's. It becomes almost a perfect copy, having the same moves as the opponent but only with 5 PP each and its stats change according to the target's. However, the Pokémon's HP and Nature stays the same. A battle between two Ditto would continue forever due to the fact that the PP get reset to 5 each time it's used.