Kanto Gym

After you defeat the all Gym Leaders,Elite 4 and Champs in Kanto Gym,You will unlock legendaries
 * Articuno
 * Zapdos
 * Moltres
 * Mewtwo
 * Mew

Gym Leaders
Brock Misty Lt. Surge Erika
 * Gives you the Boulder Badge
 * Pokemons-Level 12 Graveler and Level 14 Onix
 * Gives you the Cascade Badge
 * Pokemons-Level 18 Staryu and Level 21 Starmie
 * Gives you the Thunder Badge
 * Pokemons-Lvl 21 Voltorb,Lvl 18 Pikachu,Lvl 24 Raichu

Janine Sabrina
 * Gives you the  Rainbow Badge
 * Pokemons-Lvl 29 Victreebel,Lvl 24 Tangela,Lvl 29 Vileplume
 * Gives you the Fuchsia Badge
 * Pokemons-Lvl 42 Crobat,Lvl 39 Weezing,2  Lvl 42 Ariados and Lvl 47 Venomoth

Blaine Giovanni
 * Gives you the  Saffrom Badge
 * Pokemons-Level 38 Kadabra,Lvl 37 Mr Mime,Lvl 38 Venomoth,Lvl 43 Alakazam
 * Gives you the Volcano Badge
 * Pokemons-Lvl 42 Growlithe,Lvl 40 Ponyta,Lvl 42 Rapidash,Lvl 47 Arcanine
 * Gives you the Earth Badge
 * Pokemons-Lvl 45 Rhyhorn,Lvl 42 Dugtrio,Lvl 44 Nidoqueen,Lvl 45 Nidoking,Lvl 50 Rhyhorn

Elite 4
Lorelei Bruno Agatha Lance
 * Pokemons-Lvl 52 Dewgong,Lvl 51 Cloyster,Lvl 52 Slowbro,Lvl 54 Jynx,Lvl 54 Laparas
 * Pokemons-Lvl 51 Onix,Lvl 53 Hitmonchan,Lvl 53 Hitmonlee,Lvl 54 Onix,Lvl 56 Machamp
 * Pokemons-Lvl 54 Gengar,Lvl 54 Golbat,Lvl 53 Haunter,Lvl 56 Arbok,Lvl 58 Gengar
 * Pokemons-Lvl 56 Gyarados,2 Lvl 54 Dragonairs,Lvl 58 Aerodactyl and Lvl 60 Dragonite

Champ
Blue
 * Pokemons-Lvl 59 Pidgeot,Lvl 57 Alakazam,Lvl 59 Rhydon,Lvl 59 Arcanine,Lvl 61 Gyarados and Lvl 63 Blastoise