Route 31: 25 species in 3 games

Gold and Silver Crystal HeartGold and SoulSilver

Road 31: 25 species across 5 versions

Gold: 13 species
Species	Method	Levels	Chance	Game page
Caterpie	Walking in tall grass or a cave	4 to 5	up to 35%	All places
Metapod	Walking in tall grass or a cave	5 to 6	up to 15%	All places
Pidgey	Walking in tall grass or a cave	3	up to 30%	All places
Rattata	Walking in tall grass or a cave	4 to 5	40%	All places
Spearow	Headbutting a high encounter rate tree	10	50%	All places
Spearow	Headbutting a low encounter rate tree	10	80%	All places
Spearow	Headbutting a normal encounter rate tree	10	80%	All places
Poliwag	Fishing with a good rod	20	65%	All places
Poliwag	Fishing with an old rod	10	15%	All places
Poliwag	Fishing with a super rod	40	80%	All places
Poliwag	Surfing	15 to 24	90%	All places
Poliwhirl	Surfing	20 to 24	10%	All places
Bellsprout	Walking in tall grass or a cave	3	up to 20%	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
Hoothoot	Walking in tall grass or a cave	5	10%	All places
Spinarak	Walking in tall grass or a cave	4	30%	All places
Aipom	Headbutting a high encounter rate tree	10	20%	All places
Aipom	Headbutting a low encounter rate tree	10	20%	All places
Aipom	Headbutting a normal encounter rate tree	10	20%	All places
Heracross	Headbutting a high encounter rate tree	10	30%	All places

Silver: 13 species
Species	Method	Levels	Chance	Game page
Weedle	Walking in tall grass or a cave	4 to 5	up to 35%	All places
Kakuna	Walking in tall grass or a cave	5 to 6	up to 15%	All places
Pidgey	Walking in tall grass or a cave	3 to 5	up to 30%	All places
Rattata	Walking in tall grass or a cave	4 to 5	40%	All places
Spearow	Headbutting a high encounter rate tree	10	50%	All places
Spearow	Headbutting a low encounter rate tree	10	80%	All places
Spearow	Headbutting a normal encounter rate tree	10	80%	All places
Poliwag	Fishing with a good rod	20	65%	All places
Poliwag	Fishing with an old rod	10	15%	All places
Poliwag	Fishing with a super rod	40	80%	All places
Poliwag	Surfing	15 to 24	90%	All places
Poliwhirl	Surfing	20 to 24	10%	All places
Bellsprout	Walking in tall grass or a cave	3	up to 20%	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
Hoothoot	Walking in tall grass or a cave	3 to 5	40%	All places
Ledyba	Walking in tall grass or a cave	4	30%	All places
Aipom	Headbutting a high encounter rate tree	10	20%	All places
Aipom	Headbutting a low encounter rate tree	10	20%	All places
Aipom	Headbutting a normal encounter rate tree	10	20%	All places
Heracross	Headbutting a high encounter rate tree	10	30%	All places

Crystal: 15 species
Species	Method	Levels	Chance	Game page
Caterpie	Walking in tall grass or a cave	4 to 5	up to 50%	All places
Weedle	Walking in tall grass or a cave	4	up to 5%	All places
Pidgey	Walking in tall grass or a cave	4 to 5	up to 40%	All places
Zubat	Walking in tall grass or a cave	4	5%	All places
Poliwag	Fishing with a good rod	20	65%	All places
Poliwag	Fishing with an old rod	10	15%	All places
Poliwag	Fishing with a super rod	40	80%	All places
Poliwag	Surfing	15 to 24	90%	All places
Poliwag	Walking in tall grass or a cave	4	30%	All places
Poliwhirl	Surfing	20 to 24	10%	All places
Bellsprout	Walking in tall grass or a cave	5	20%	All places
Gastly	Walking in tall grass or a cave	5	5%	All places
Exeggcute	Headbutting a high encounter rate tree	10	20%	All places
Exeggcute	Headbutting a low encounter rate tree	10	20%	All places
Exeggcute	Headbutting a normal encounter rate tree	10	20%	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
Hoothoot	Headbutting a high encounter rate tree	10	50%	All places
Hoothoot	Headbutting a low encounter rate tree	10	50%	All places
Hoothoot	Headbutting a normal encounter rate tree	10	50%	All places
Hoothoot	Walking in tall grass or a cave	5	10%	All places
Ledyba	Headbutting a low encounter rate tree	10	15%	All places
Ledyba	Headbutting a normal encounter rate tree	10	15%	All places
Ledyba	Walking in tall grass or a cave	4	30%	All places
Spinarak	Headbutting a low encounter rate tree	10	15%	All places
Spinarak	Headbutting a normal encounter rate tree	10	15%	All places
Spinarak	Walking in tall grass or a cave	4	30%	All places
Hoppip	Walking in tall grass or a cave	5	up to 5%	All places
Pineco	Headbutting a high encounter rate tree	10	30%	All places

HeartGold: 16 species
Species	Method	Levels	Chance	Game page
Caterpie	Walking in tall grass or a cave	4 to 5	up to 25%	All places
Metapod	Walking in tall grass or a cave	5	up to 15%	All places
Pidgey	Walking in tall grass or a cave	3	up to 20%	All places
Rattata	Walking in tall grass or a cave	4 to 5	up to 30%	All places
Poliwag	Fishing with a good rod	20	60%	All places
Poliwag	Fishing with an old rod	10	15%	All places
Poliwag	Fishing with a super rod	40	80%	All places
Poliwag	Surfing	10 to 25	90%	All places
Poliwhirl	Surfing	15 to 32	10%	All places
Bellsprout	Walking in tall grass or a cave	3	20%	All places
Exeggcute	Headbutting trees	3 to 6	up to 20%	All places
Magikarp	Fishing with a good rod	20	40%	All places
Magikarp	Fishing with an old rod	10	85%	All places
Magikarp	Fishing with a super rod	40	20%	All places
Hoothoot	Headbutting trees	3 to 6	up to 50%	All places
Hoothoot	Walking in tall grass or a cave	5	10%	All places
Spinarak	Headbutting trees	5 to 6	30%	All places
Spinarak	Walking in tall grass or a cave	3	up to 20%	All places
Pineco	Headbutting trees	3 to 4	30%	All places
Linoone	Walking in tall grass or a cave	3	20%	All places
Whismur	Walking in tall grass or a cave	3 to 4	20%	All places
Bidoof	Walking in tall grass or a cave	3	20%	All places
Buizel	Walking in tall grass or a cave	3 to 4	20%	All places

SoulSilver: 16 species
Species	Method	Levels	Chance	Game page
Weedle	Walking in tall grass or a cave	4 to 5	up to 25%	All places
Kakuna	Walking in tall grass or a cave	5	up to 15%	All places
Pidgey	Walking in tall grass or a cave	4 to 5	up to 20%	All places
Rattata	Walking in tall grass or a cave	4 to 5	up to 30%	All places
Poliwag	Fishing with a good rod	20	60%	All places
Poliwag	Fishing with an old rod	10	15%	All places
Poliwag	Fishing with a super rod	40	80%	All places
Poliwag	Surfing	10 to 25	90%	All places
Poliwhirl	Surfing	15 to 32	10%	All places
Bellsprout	Walking in tall grass or a cave	3	20%	All places
Exeggcute	Headbutting trees	3 to 6	up to 20%	All places
Magikarp	Fishing with a good rod	20	40%	All places
Magikarp	Fishing with an old rod	10	85%	All places
Magikarp	Fishing with a super rod	40	20%	All places
Hoothoot	Headbutting trees	3 to 6	up to 50%	All places
Hoothoot	Walking in tall grass or a cave	4 to 5	up to 30%	All places
Ledyba	Headbutting trees	5 to 6	30%	All places
Ledyba	Walking in tall grass or a cave	4	up to 20%	All places
Pineco	Headbutting trees	3 to 4	30%	All places
Linoone	Walking in tall grass or a cave	3	20%	All places
Whismur	Walking in tall grass or a cave	4	20%	All places
Bidoof	Walking in tall grass or a cave	3	20%	All places
Buizel	Walking in tall grass or a cave	4	20%	All places