Instructions
Select a Pokemon that can use Night Slash. (See Resources for a list of the 30 Pokemon that can use Night Slash; another 18 can be bred to learn the move.)
Raise the levels of your chosen Pokemon through battle until it can learn Night Slash. The level at which your Pokemon can learn Night Slash will vary from Pokemon to Pokemon. For example, at level 37, Stunky will learn Night Slash but Meowth does not learn it until level 49.
Enter a battle with the Pokemon that has learned Night Slash.
Tap "Fight" on the Nintendo DS's lower screen.
Tap "Night Slash." The move will now be performed. Night Slash can be used a maximum of fifteen times, across all battles, before you must rest your Pokemon at the Pokemon Center.