Crystal Gym Leaders & Elite Four
As usual, in Crystal you battle your way through 8 gyms, each specializing in a particular type. Following that you take on the Elite Four and the Champion. In fact all the teams and levels are the game as Gold/Silver.
The 8 gyms in Johto are different types to those in Kanto, and the Elite Four has some changes from generation 1.
Gym #1, Violet City
Gym #2, Azalea Town

Bugsy
Hive Badge
Bug type Pokémon
Gym #3, Goldenrod City
Gym #4, Ecruteak City

Morty
Fog Badge
Ghost type Pokémon
Gym #5, Cianwood City

Chuck
Storm Badge
Fighting type Pokémon
Gym #6, Olivine City

Jasmine
Mineral Badge
Steel type Pokémon
Gym #7, Mahogany Town

Pryce
Glacier Badge
Ice type Pokémon
Gym #8, Blackthorn City

Clair
Rising Badge
Dragon type Pokémon
Gym #9, Pewter City

Brock
Boulder Badge
Rock type Pokémon
Gym #10, Cerulean City

Misty
Cascade Badge
Water type Pokémon
Gym #11, Vermilion City

Lt. Surge
Thunder Badge
Electric type Pokémon

Electabuzz
Level 46
Electric
Gym #12, Celadon City

Erika
Rainbow Badge
Grass type Pokémon

Victreebel
Level 46
Grass · Poison
Gym #13, Fuchsia City

Janine
Soul Badge
Poison type Pokémon
Gym #14, Saffron City

Sabrina
Marsh Badge
Psychic type Pokémon
Gym #15, Cinnabar Island

Blaine
Volcano Badge
Fire type Pokémon
Gym #16, Viridian City

Blue
Earth Badge
Mixed types
Elite Four #1

Will
Psychic type Pokémon
Elite Four #2

Koga
Poison type Pokémon

Forretress
Level 43
Bug · Steel
Elite Four #3

Bruno
Fighting type Pokémon

Hitmonchan
Level 42
Fighting
Elite Four #4

Karen
Dark type Pokémon
Champion

Lance
Dragon type Pokémon

Aerodactyl
Level 46
Rock · Flying