Things You'll Need
Instructions
Use your Pokemon's "Fly" ability to travel to Cinnabar Island. If your Pokemon does not have the ability, you can use "Surf," as well, though it will take much longer to arrive at Cinnabar Island.
Walk around the Pokemon Center. Depending on the time of day, Gary will be in different parts of the island but near the Pokemon Center.
Talk with him to get him to return to his gym in Viridian City.
Fly to Viridian City and enter the gym. You must battle the trainers before you can battle Gary to obtain your sixteenth and final badge.