Instructions
Defeat all of the final trainers in the Pokemon League, then fly to Pewter City.
Talk to the old man in the southeastern part of the city. You will receive a Silver Feather.
Head to the Whirl Islands, located near Cianwood City. Travel to the northeastern most island in the area.
Enter the cave, then head to the northeastern ladder on the first floor. Reach the second floor, then follow the path south, west, then south again to reach the next ladder.
Head to the southern cave entrance on the third floor. Once you enter the cave, you will see Lugia.
Engage Lugia. Use any combination of attacks to decrease its hit points. Avoid using damage over time skills like Poison.
Throw Ultraballs or Heavy Balls at Lugia. If the legendary Pokemon still resists a capture, use status ailments like Sleep or Paralyze. Continue repeating steps six and seven until Lugia has been successfully caught.