Zoroark

With a respectable base 105 Attack and base 120 Special Attack, and enough of a movepool to utilize them, Zoroark can do some serious damage if left alone. However, with its poor base 60 / 60 / 60 defenses, Zoroark can be OHKOed by powerful STAB moves. Fortunately for Zoroark, its unique ability, Illusion, helps it out both offensively and defensively. Illusion lets Zoroark masquerade as the last Pokemon selected in a team of four. However, thanks to Team Preview, the opponent will still be alerted to Zoroark's existence. While some might say that Team Preview ruins Zoroark's surprise factor, simply knowing that Zoroark might show up does not say anything about when it will actually reveal itself, or if it is even in the battle at all. With the right timing and the right Illusion, this master of disguise will leave the opponent wondering what just hit them.