Ditto

With Imposter and a Choice Scarf, Ditto is an excellent revenge killer on Normal teams that is able to immediately change the outcome of a game. This is thanks to its ability to copy stat boosts of the foe, therefore discouraging the opponent from setting up. Ditto also works well as a scout, easing predictions, and it can also fit onto stall teams that need a Pokemon that can play mind games on and annoy the opposing team. However, the opponent can simply switch out its Pokemon and bring out a counter to the Pokemon that Ditto has transformed into. Furthermore, Ditto's unpredictability might not always be in your favor, as the foe might have a bad moveset to copy, forcing Ditto to switch out due to being dead weight and sapping a lot of momentum. In addition, the opponent knows what set their own Pokemon is running, so they can exploit this by playing around Ditto easily. Ditto's moves also have only 5 PP, so the foe can easily stall them out by using recovery moves. Finally, Ditto does not copy the foe's HP stat, leaving it forced to cope with its own appalling base 48 HP.