National Park: 35 species in 3 games

Gold and Silver Crystal HeartGold and SoulSilver

35 species, 5 versions

Gold and SilverCrystalHeartGold and SoulSilver

Gold and Silver: 5 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Caterpie	10 to 12	up to 50%	All places
Metapod	10	up to 30%	All places
Pidgey	10 to 14	up to 20%	All places
Hoothoot	10 to 14	100%	All places
Sunkern	12 to 13	25%	All places

Crystal: 11 species, all by walking in tall grass or a cave
Species	Levels	Chance	Game page
Caterpie	10	up to 5%	All places
Weedle	10	up to 5%	All places
Pidgey	13	up to 10%	All places
Nidoran♀	12	up to 30%	All places
Nidoran♂	12	up to 30%	All places
Venonat	10	10%	All places
Psyduck	12	30%	All places
Hoothoot	12 to 15	40%	All places
Ledyba	14	20%	All places
Spinarak	14	20%	All places
Sunkern	14	20%	All places

HeartGold and SoulSilver: 31 species
Species	Method	Levels	Chance	Game page
Caterpie	Walking in tall grass or a cave	7 to 36	up to 30%	All places
Metapod	Walking in tall grass or a cave	9 to 36	up to 20%	All places
Butterfree	Walking in tall grass or a cave	12 to 30	up to 5%	All places
Weedle	Walking in tall grass or a cave	7 to 36	up to 20%	All places
Kakuna	Walking in tall grass or a cave	9 to 36	up to 10%	All places
Beedrill	Walking in tall grass or a cave	12 to 30	up to 5%	All places
Pidgey	Walking in tall grass or a cave	10 to 14	up to 20%	All places
Paras	Walking in tall grass or a cave	10 to 34	up to 10%	All places
Venonat	Walking in tall grass or a cave	10 to 32	up to 10%	All places
Exeggcute	Headbutting trees	10 to 20	up to 65%	All places
Scyther	Walking in tall grass or a cave	13 to 28	up to 5%	All places
Pinsir	Walking in tall grass or a cave	13 to 28	up to 5%	All places
Hoothoot	Headbutting trees	10 to 15	up to 50%	All places
Hoothoot	Walking in tall grass or a cave	10 to 14	up to 60%	All places
Spinarak	Headbutting trees	13 to 15	30%	All places
Sunkern	Walking in tall grass or a cave	10 to 12	up to 20%	All places
Pineco	Headbutting trees	10 to 12	30%	All places
Wurmple	Walking in tall grass or a cave	24 to 36	up to 20%	All places
Silcoon	Walking in tall grass or a cave	24 to 36	10%	All places
Beautifly	Walking in tall grass or a cave	25 to 32	5%	All places
Cascoon	Walking in tall grass or a cave	24 to 36	10%	All places
Dustox	Walking in tall grass or a cave	25 to 32	5%	All places
Nincada	Walking in tall grass or a cave	26 to 36	up to 20%	All places
Plusle	Walking in tall grass or a cave	10	20%	All places
Minun	Walking in tall grass or a cave	12	20%	All places
Volbeat	Walking in tall grass or a cave	26 to 36	10%	All places
Illumise	Walking in tall grass or a cave	26 to 36	10%	All places
Kricketot	Walking in tall grass or a cave	27 to 30	up to 10%	All places
Kricketune	Walking in tall grass or a cave	27 to 30	up to 10%	All places
Shinx	Walking in tall grass or a cave	10 to 12	40%	All places
Combee	Walking in tall grass or a cave	27 to 34	up to 5%	All places
Cherubi	Headbutting trees	18 to 25	35%	All places