Instructions
Leave Violet City from the southwest exit to enter the Ruins of Alph area.
Walk through the tall grass outside of the caves until you find a Natu. You will encounter a wild Natu 90 percent of the time when you meet a wild Pokemon in this area.
Disable the Natu with techniques such as Hypnosis and Thunderwave. When a Natu is sleeping, paralyzed or frozen, it becomes easier to capture in a Poke Ball. When its health meter turns red from taking damage, throw a Poke Ball to catch the Natu.