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Deals damage and has a 20% chance to lower the target's Defense by one stage.
One of the best physical Dark-type moves available. It has a decent Base Power, good distribution, and a excellent side effect, and can be used as a main STAB option or even as a coverage move. Note that if paired with a Fighting-type move it gains almost perfect neutral coverage, only resisted by Heracross and Toxicroak. The most common user is Tyranitar, thanks to an amazing Attack stat and a Dark typing, which enables it to crush almost anything. The secondary effect comes in useful too, which can enable Tyranitar to win prolonged stalling wars by reducing its opponent's Defense, so that Crunch does even more damage. It is also fairly widespread as a move, despite not being a TM.
Night Slash is a less powerful option that has a higher critical hit rate.
Sucker Punch has the same Base Power and +1 priority, but the opponent needs to select a damaging move for it to be successful.