Route 18: 38 species

Red and Green (Japan): 9 species
Species	Method	Levels	Chance	Game page
Raticate	Walking in tall grass or a cave	25 to 29	20%	All places
Spearow	Walking in tall grass or a cave	20 to 22	40%	All places
Fearow	Walking in tall grass or a cave	25 to 29	15%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Tentacool	Fishing with a super rod	5	25%	All places
Doduo	Walking in tall grass or a cave	24 to 28	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

Red and Blue: 10 species
Species	Method	Levels	Chance	Game page
Raticate	Walking in tall grass or a cave	25 to 29	20%	All places
Spearow	Walking in tall grass or a cave	20 to 22	40%	All places
Fearow	Walking in tall grass or a cave	25 to 29	15%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Tentacool	Fishing with a super rod	5	25%	All places
Doduo	Walking in tall grass or a cave	24 to 28	25%	All places
Krabby	Fishing with a super rod	15	25%	All places
Lickitung	Trade with an npc	23 to 100	100%	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

Yellow: 11 species
Species	Method	Levels	Chance	Game page
Rattata	Walking in tall grass or a cave	23 to 24	25%	All places
Raticate	Walking in tall grass or a cave	25 to 26	5%	All places
Spearow	Walking in tall grass or a cave	22 to 23	25%	All places
Fearow	Walking in tall grass or a cave	24	5%	All places
Parasect	Trade with an npc	22 to 100	100%	All places
Poliwag	Fishing with a good rod	10	50%	All places
Tentacool	Fishing with a super rod	15	40%	All places
Doduo	Walking in tall grass or a cave	22 to 26	40%	All places
Shellder	Fishing with a super rod	20 to 40	60%	All places
Goldeen	Fishing with a good rod	10	50%	All places
Magikarp	Fishing with an old rod	5	100%	All places

Gold: 5 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Fearow	27 to 29	up to 40%	All places
Grimer	26 to 28	up to 80%	All places
Muk	30	up to 5%	All places
Murkrow	28	10%	All places
Slugma	27	up to 5%	All places

Silver: 5 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Fearow	27 to 29	up to 40%	All places
Grimer	26 to 28	up to 80%	All places
Muk	30	up to 5%	All places
Murkrow	28	10%	All places
Slugma	27	up to 5%	All places

Crystal: 4 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Fearow	27 to 29	up to 45%	All places
Grimer	26 to 29	up to 95%	All places
Muk	30	up to 5%	All places
Slugma	29	5%	All places

FireRed: 6 species
Species	Method	Levels	Chance	Game page
Rattata	Walking in tall grass or a cave	22	5%	All places
Raticate	Walking in tall grass or a cave	25 to 29	15%	All places
Spearow	Walking in tall grass or a cave	20 to 22	30%	All places
Fearow	Walking in tall grass or a cave	25 to 29	15%	All places
Doduo	Walking in tall grass or a cave	24 to 28	35%	All places
Lickitung	Trade with an npc	33 to 100	100%	All places

LeafGreen: 6 species
Species	Method	Levels	Chance	Game page
Rattata	Walking in tall grass or a cave	22	5%	All places
Raticate	Walking in tall grass or a cave	25 to 29	15%	All places
Spearow	Walking in tall grass or a cave	20 to 22	30%	All places
Fearow	Walking in tall grass or a cave	25 to 29	15%	All places
Doduo	Walking in tall grass or a cave	24 to 28	35%	All places
Lickitung	Trade with an npc	25 to 100	100%	All places

HeartGold and SoulSilver: 11 species
Species	Method	Levels	Chance	Game page
Fearow	Walking in tall grass or a cave	27 to 29	up to 30%	All places
Grimer	Walking in tall grass or a cave	26 to 28	up to 30%	All places
Muk	Walking in tall grass or a cave	29 to 30	up to 10%	All places
Tangela	Headbutting trees	29 to 30	15%	All places
Hoothoot	Headbutting trees	26 to 30	up to 65%	All places
Spinarak	Headbutting trees	26 to 27	30%	All places
Slugma	Walking in tall grass or a cave	27	5%	All places
Wurmple	Headbutting trees	26 to 30	up to 20%	All places
Plusle	Walking in tall grass or a cave	26 to 27	20%	All places
Minun	Walking in tall grass or a cave	28	20%	All places
Shinx	Walking in tall grass or a cave	26 to 28	40%	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	33 to 38	100%	All places
Pidgey	Flying pokemon in the sky	3 to 56	100%	All places
Pidgeotto	Walking in the overworld	33 to 38	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	33 to 38	100%	All places
Raticate	Walking in the overworld	33 to 38	100%	All places
Tentacool	Surfing in the overworld	33 to 38	100%	All places
Tentacruel	Surfing in the overworld	33 to 38	100%	All places
Doduo	Walking in the overworld	33 to 38	100%	All places
Dodrio	Walking in the overworld	33 to 38	100%	All places
Chansey	Rare spawn in grass with lure or catch combo	33 to 38	100%	All places
Staryu	Surfing in the overworld	33 to 38	100%	All places
Starmie	Surfing in the overworld	33 to 38	100%	All places
Magikarp	Surfing in the overworld	33 to 38	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

Route 18: 38 species in 8 games