Eight badges are required to enter the Indigo League in the original Pokémon TV series.
Trainers must collect eight official Gym Badges from Kanto Gym Leaders before they can compete in the Indigo Plateau Conference. The badges demonstrate that a trainer has completed the region’s Gym challenge and is eligible for the League tournament.
The eight Kanto badges are the Boulder, Cascade, Thunder, Rainbow, Soul, Marsh, Volcano, and Earth Badges. Ash’s journey includes unusual circumstances around several badges, including gifts or victories connected with events beyond a straightforward battle.
The Indigo League should not be confused with the Indigo Plateau itself, which hosts the conference. The number eight is also the standard badge requirement used for many later regional League challenges, although individual story structures can vary.