Route 11: 42 species in 8 games

Road 11: 42 species across 14 versions

Red and Green (Japan): 8 species
Species	Method	Levels	Chance	Game page
Spearow	Walking in tall grass or a cave	13 to 17	35%	All places
Ekans	Walking in tall grass or a cave	12 to 15	40%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Shellder	Fishing with a super rod	15	50%	All places
Drowzee	Walking in tall grass or a cave	9 to 15	25%	All places
Krabby	Fishing with a super rod	15	50%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Magikarp	Fishing with an old rod	5	100%	All places

Red and Blue: 9 species
Species	Method	Levels	Chance	Game page
Spearow	Walking in tall grass or a cave	13 to 17	35%	All places
Ekans	Walking in tall grass or a cave	12 to 15	40%	All places
Nidorina	Trade with an npc	16 to 100	100%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Shellder	Fishing with a super rod	15	50%	All places
Drowzee	Walking in tall grass or a cave	9 to 15	25%	All places
Krabby	Fishing with a super rod	15	50%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Magikarp	Fishing with an old rod	5	100%	All places

Yellow: 11 species
Species	Method	Levels	Chance	Game page
Pidgey	Walking in tall grass or a cave	16 to 18	35%	All places
Pidgeotto	Walking in tall grass or a cave	18 to 20	10%	All places
Rattata	Walking in tall grass or a cave	15 to 17	30%	All places
Raticate	Walking in tall grass or a cave	17	1%	All places
Dugtrio	Trade with an npc	50 to 100	100%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Tentacool	Fishing with a super rod	10 to 20	90%	All places
Drowzee	Walking in tall grass or a cave	15 to 19	24%	All places
Horsea	Fishing with a super rod	5	10%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Magikarp	Fishing with an old rod	5	100%	All places

Gold and Silver: 4 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Rattata	15	30%	All places
Magnemite	15	20%	All places
Drowzee	14 to 16	40%	All places
Hypno	16	10%	All places

Crystal: 9 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Pidgeotto	16	up to 10%	All places
Rattata	16	up to 5%	All places
Raticate	15 to 16	up to 30%	All places
Meowth	15	30%	All places
Magnemite	15	up to 20%	All places
Drowzee	14	30%	All places
Hypno	16	5%	All places
Noctowl	16	10%	All places
Hoppip	14 to 16	up to 35%	All places

FireRed: 10 species
Species	Method	Levels	Chance	Game page
Spearow	Walking in tall grass or a cave	13 to 17	35%	All places
Ekans	Walking in tall grass or a cave	12 to 15	40%	All places
Nidorina	Trade with an npc	16 to 100	100%	All places
Psyduck	Fishing with a super rod	25 to 35	1%	All places
Tentacool	Surfing	5 to 40	100%	All places
Drowzee	Walking in tall grass or a cave	11 to 15	25%	All places
Krabby	Fishing with a good rod	5 to 15	20%	All places
Horsea	Fishing with a good rod	5 to 15	60%	All places
Horsea	Fishing with a super rod	15 to 35	84%	All places
Magikarp	Fishing with a good rod	5 to 15	20%	All places
Magikarp	Fishing with an old rod	5	100%	All places
Gyarados	Fishing with a super rod	15 to 25	15%	All places

LeafGreen: 10 species
Species	Method	Levels	Chance	Game page
Spearow	Walking in tall grass or a cave	13 to 17	35%	All places
Sandshrew	Walking in tall grass or a cave	12 to 15	40%	All places
Nidorino	Trade with an npc	16 to 100	100%	All places
Tentacool	Surfing	5 to 40	100%	All places
Slowpoke	Fishing with a super rod	25 to 35	1%	All places
Drowzee	Walking in tall grass or a cave	11 to 15	25%	All places
Krabby	Fishing with a good rod	5 to 15	60%	All places
Krabby	Fishing with a super rod	15 to 35	84%	All places
Horsea	Fishing with a good rod	5 to 15	20%	All places
Magikarp	Fishing with a good rod	5 to 15	20%	All places
Magikarp	Fishing with an old rod	5	100%	All places
Gyarados	Fishing with a super rod	15 to 25	15%	All places

HeartGold and SoulSilver: 11 species
Species	Method	Levels	Chance	Game page
Rattata	Walking in tall grass or a cave	15	up to 20%	All places
Spearow	Headbutting trees	13 to 16	up to 80%	All places
Magnemite	Walking in tall grass or a cave	15	20%	All places
Drowzee	Walking in tall grass or a cave	14 to 16	up to 30%	All places
Hypno	Walking in tall grass or a cave	16	10%	All places
Snorlax	Playing pokéflute	50	100%	All places
Heracross	Headbutting trees	13 to 14	30%	All places
Plusle	Walking in tall grass or a cave	14 to 15	20%	All places
Minun	Walking in tall grass or a cave	15	20%	All places
Shinx	Walking in tall grass or a cave	14 to 15	40%	All places
Combee	Headbutting trees	13 to 16	up to 20%	All places

Let's Go, Pikachu and Eevee: 18 species
Species	Method	Levels	Chance	Game page
Charizard	Rare spawn in the sky with lure or catch combo	3 to 56	100%	All places
Pidgey	Walking in the overworld	13 to 18	100%	All places
Pidgey	Flying pokemon in the sky	3 to 56	100%	All places
Pidgeotto	Walking in the overworld	13 to 18	100%	All places
Pidgeotto	Flying pokemon in the sky	3 to 56	100%	All places
Pidgeot	Flying pokemon in the sky	3 to 56	100%	All places
Rattata	Walking in the overworld	13 to 18	100%	All places
Raticate	Walking in the overworld	13 to 18	100%	All places
Tentacool	Surfing in the overworld	13 to 18	100%	All places
Tentacruel	Surfing in the overworld	13 to 18	100%	All places
Drowzee	Walking in the overworld	13 to 18	100%	All places
Chansey	Rare spawn in grass with lure or catch combo	13 to 18	100%	All places
Horsea	Surfing in the overworld	13 to 18	100%	All places
Seadra	Surfing in the overworld	13 to 18	100%	All places
Mr. Mime	Walking in the overworld	13 to 18	100%	All places
Magikarp	Surfing in the overworld	13 to 18	100%	All places
Articuno	Rare spawn in the sky with lure or catch combo	3 to 56	100%	All places
Zapdos	Rare spawn in the sky with lure or catch combo	3 to 56	100%	All places
Moltres	Rare spawn in the sky with lure or catch combo	3 to 56	100%	All places
Dragonite	Rare spawn in the sky with lure or catch combo	3 to 56	100%	All places