Members of Team Go Rocket may be discovered on hot air balloons hovering above you or in glitchy, black PokéStops. You’ll gain a Mysterious Component every time you beat one. When you collect 6 Mysterious Components, they will combine to become a Rocket Radar, allowing you to locate a random leader. Sierra, Arlo, and Cliff are the three leaders.
Some Timely Research and Collaboration Go Rocket Special Research assignments need defeating all three leaders. Occasionally, but not usually, you’ll be awarded with a Super Rocket Radar, which will enable you to locate the boss, Giovanni. Beating Giovanni will provide you access to a Legendary Shadow Pokémon.