Route 12: 37 species in 8 games

Road 12: 37 species across 14 versions

Red and Green (Japan): 10 species
Species	Method	Levels	Chance	Game page
Pidgey	Walking in tall grass or a cave	23 to 27	40%	All places
Oddish	Walking in tall grass or a cave	22 to 26	35%	All places
Gloom	Walking in tall grass or a cave	28 to 30	5%	All places
Venonat	Walking in tall grass or a cave	24 to 26	20%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Tentacool	Fishing with a super rod	5	25%	All places
Krabby	Fishing with a super rod	15	25%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Goldeen	Fishing with a super rod	15	25%	All places
Magikarp	Fishing with an old rod	5	100%	All places
Magikarp	Fishing with a super rod	15	25%	All places
Snorlax	Playing pokéflute	30	100%	All places

Red and Blue: 10 species
Species	Method	Levels	Chance	Game page
Pidgey	Walking in tall grass or a cave	23 to 27	40%	All places
Oddish	Walking in tall grass or a cave	22 to 26	35%	All places
Gloom	Walking in tall grass or a cave	28 to 30	5%	All places
Venonat	Walking in tall grass or a cave	24 to 26	20%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Tentacool	Fishing with a super rod	5	25%	All places
Krabby	Fishing with a super rod	15	25%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Goldeen	Fishing with a super rod	15	25%	All places
Magikarp	Fishing with an old rod	5	100%	All places
Magikarp	Fishing with a super rod	15	25%	All places
Snorlax	Playing pokéflute	30	100%	All places

Yellow: 15 species
Species	Method	Levels	Chance	Game page
Pidgey	Walking in tall grass or a cave	28	15%	All places
Pidgeotto	Walking in tall grass or a cave	28	10%	All places
Oddish	Walking in tall grass or a cave	25 to 27	30%	All places
Gloom	Walking in tall grass or a cave	29	5%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Bellsprout	Walking in tall grass or a cave	25 to 27	30%	All places
Weepinbell	Walking in tall grass or a cave	29	5%	All places
Slowpoke	Surfing	15	95%	All places
Slowbro	Surfing	15 to 20	5%	All places
Farfetch’d	Walking in tall grass or a cave	26 to 31	5%	All places
Horsea	Fishing with a super rod	20 to 25	70%	All places
Seadra	Fishing with a super rod	25 to 35	30%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Magikarp	Fishing with an old rod	5	100%	All places
Snorlax	Playing pokéflute	30	100%	All places

Gold and Silver: 5 species
Species	Method	Levels	Chance	Game page
Tentacool	Fishing with a good rod	20	65%	All places
Tentacool	Fishing with an old rod	10	15%	All places
Tentacool	Fishing with a super rod	40	70%	All places
Tentacool	Surfing	25 to 29	60%	All places
Tentacruel	Surfing	25 to 29	10%	All places
Magikarp	Fishing with a good rod	20	35%	All places
Magikarp	Fishing with an old rod	10	85%	All places
Magikarp	Fishing with a super rod	40	20%	All places
Quagsire	Surfing	25 to 29	30%	All places
Qwilfish	Fishing with a super rod	40	10%	All places

Crystal: 5 species
Species	Method	Levels	Chance	Game page
Tentacool	Fishing with a good rod	20	65%	All places
Tentacool	Fishing with an old rod	10	15%	All places
Tentacool	Fishing with a super rod	40	70%	All places
Tentacool	Surfing	25 to 29	60%	All places
Tentacruel	Surfing	25 to 29	10%	All places
Magikarp	Fishing with a good rod	20	35%	All places
Magikarp	Fishing with an old rod	10	85%	All places
Magikarp	Fishing with a super rod	40	20%	All places
Quagsire	Surfing	25 to 29	30%	All places
Qwilfish	Fishing with a super rod	40	10%	All places

FireRed: 11 species
Species	Method	Levels	Chance	Game page
Pidgey	Walking in tall grass or a cave	23 to 27	30%	All places
Oddish	Walking in tall grass or a cave	22 to 26	35%	All places
Gloom	Walking in tall grass or a cave	28 to 30	5%	All places
Venonat	Walking in tall grass or a cave	24 to 26	30%	All places
Psyduck	Fishing with a super rod	25 to 35	1%	All places
Tentacool	Surfing	5 to 40	100%	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
Snorlax	Playing pokéflute	30	100%	All places

LeafGreen: 11 species
Species	Method	Levels	Chance	Game page
Pidgey	Walking in tall grass or a cave	23 to 27	30%	All places
Venonat	Walking in tall grass or a cave	24 to 26	30%	All places
Bellsprout	Walking in tall grass or a cave	22 to 26	35%	All places
Weepinbell	Walking in tall grass or a cave	28 to 30	5%	All places
Tentacool	Surfing	5 to 40	100%	All places
Slowpoke	Fishing with a super rod	25 to 35	1%	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
Snorlax	Playing pokéflute	30	100%	All places

HeartGold and SoulSilver: 11 species
Species	Method	Levels	Chance	Game page
Tentacool	Fishing with a good rod	20	up to 35%	All places
Tentacool	Fishing with an old rod	10	15%	All places
Tentacool	Fishing with a super rod	40	70%	All places
Tentacool	Surfing	25	60%	All places
Tentacruel	Surfing	25	10%	All places
Tangela	Headbutting trees	24 to 25	15%	All places
Magikarp	Fishing with a good rod	20	40%	All places
Magikarp	Fishing with an old rod	10	up to 70%	All places
Magikarp	Fishing with a super rod	40	20%	All places
Snorlax	Playing pokéflute	50	100%	All places
Hoothoot	Headbutting trees	22 to 25	up to 65%	All places
Spinarak	Headbutting trees	22 to 23	30%	All places
Quagsire	Surfing	25	30%	All places
Qwilfish	Fishing with a super rod	40	10%	All places
Wurmple	Headbutting trees	22 to 25	up to 20%	All places
Relicanth	Fishing with a good rod	20	65%	All places
Relicanth	Fishing with an old rod	10	15%	All places
Relicanth	Fishing with a super rod	40	100%	All places

Let's Go, Pikachu and Eevee: 20 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	31 to 36	100%	All places
Pidgey	Flying pokemon in the sky	3 to 56	100%	All places
Pidgeotto	Walking in the overworld	31 to 36	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
Oddish	Walking in the overworld	31 to 36	100%	All places
Gloom	Walking in the overworld	31 to 36	100%	All places
Tentacool	Surfing in the overworld	31 to 36	100%	All places
Tentacruel	Surfing in the overworld	31 to 36	100%	All places
Farfetch’d	Walking in the overworld	31 to 36	100%	All places
Krabby	Walking in the overworld	31 to 36	100%	All places
Kingler	Walking in the overworld	31 to 36	100%	All places
Chansey	Rare spawn in grass with lure or catch combo	31 to 36	100%	All places
Horsea	Surfing in the overworld	31 to 36	100%	All places
Seadra	Surfing in the overworld	31 to 36	100%	All places
Magikarp	Surfing in the overworld	31 to 36	100%	All places
Snorlax	Playing pokéflute	34	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