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RGBY Minimum Levels

This page lists the lowest possible level at which you can obtain Pokémon in Red, Green, Blue, and Yellow.

The table below lists the lowest levels that each Pokémon is obtainable without trading with another game.

RBY Minimum Levels (Each Game Alone)
Pokémon Games Level Location(s)
Bulbasaur
Bulbasaur R B Y 5 Gift: Pallet Town
R B Y 10 Gift: Cerulean City
Ivysaur
Ivysaur R B Y 16 Evolve Bulbasaur
Venusaur
Venusaur R B Y 32 Evolve Ivysaur
Charmander
Charmander R B Y 5 Gift: Pallet Town
R B Y 10 Gift: Route 24
Charmeleon
Charmeleon R B Y 16 Evolve Charmander
Charizard
Charizard R B Y 36 Evolve Charmeleon
Squirtle
Squirtle R B Y 5 Gift: Pallet Town
R B Y 10 Gift: Vermilion City
Wartortle
Wartortle R B Y 16 Evolve Squirtle
Blastoise
Blastoise R B Y 36 Evolve Wartortle
Caterpie
Caterpie R B Y 3 Walking: Viridian Forest
R B Y 3 Walking: Route 2 and Viridian Forest
Metapod
Metapod R B Y 4 Walking: Viridian Forest
Butterfree
Butterfree R B Y 10 Evolve Metapod
Weedle
Weedle R B Y 3 Walking: Route 2 and Viridian Forest
R B Y 3 Walking: Viridian Forest
Kakuna
Kakuna R B Y 4 Walking: Viridian Forest
Beedrill
Beedrill R B Y 10 Evolve Kakuna
Pidgey
Pidgey R B Y 2 Walking: Route 1
Pidgeotto
Pidgeotto R B Y 18 Evolve Pidgey
R B Y 9 Walking: Viridian Forest
Pidgeot
Pidgeot R B Y 36 Evolve Pidgeotto
Rattata
Rattata R B Y 2 Walking: Routes 1, 2, and 22
R B Y 2 Walking: Route 1
Raticate
Raticate R B Y 20 Evolve Rattata
R B Y 15 Walking: Route 21
Spearow
Spearow R B Y 3 Walking: Route 22
R B Y 2 Walking: Route 22
Fearow
Fearow R B Y 20 Evolve Spearow
R B Y 19 Walking: Route 9
Ekans
Ekans R B Y 6 Walking: Route 4
Arbok
Arbok R B Y 22 Evolve Ekans
Pikachu
Pikachu R B Y 3 Walking: Viridian Forest
R B Y 5 Gift: Pallet Town
Raichu
Raichu R B Y 3 Evolve Pikachu
Sandshrew
Sandshrew R B Y 6 Walking: Route 4
R B Y 8 Walking: Routes 3 and 4
Sandslash
Sandslash R B Y 22 Evolve Sandshrew
Nidoran♀
Nidoran♀ R B Y 2 In-Game Trade: Route 5-6 Underground Path (trade a level 2 Nidoran♂)
R B Y 2 Walking: Route 22
Nidorina
Nidorina R B Y 16 Evolve Nidoran♀
R B Y 16 In-Game Trade: Route 11 (trade a level 16 Nidorino)
Nidoqueen
Nidoqueen R B Y 16 Evolve Nidorina
Nidoran♂
Nidoran♂ R B Y 2 Walking: Route 22
R B Y 3 Walking: Route 22
Nidorino
Nidorino R B Y 16 Evolve Nidoran♂
Nidoking
Nidoking R B Y 16 Evolve Nidorino
Clefairy
Clefairy R B Y 8 Walking: Mt. Moon (1F)
Purchase: Celadon Game Corner
R B Y 8 Walking: Mt. Moon (1F)
R B Y 9 Walking: Mt. Moon (B2F)
Clefable
Clefable R B Y 8 Evolve Clefairy
R B Y 9 Evolve Clefairy
Vulpix
Vulpix R B Y 15 Walking: Route 8
R B Y 18 Purchase: Celadon Game Corner
Ninetales
Ninetales R B Y 15 Evolve Vulpix
R B Y 18 Evolve Vulpix
Jigglypuff
Jigglypuff R B Y 3 Walking: Route 3
R B Y 3 Walking: Routes 5 and 6
Wigglytuff
Wigglytuff R B Y 3 Evolve Jigglypuff
Zubat
Zubat R B Y 6 Walking: Mt. Moon (1F)
Golbat
Golbat R B Y 22 Evolve Zubat
Oddish
Oddish R B Y 12 Walking: Routes 24 and 25
Gloom
Gloom R B Y 21 Evolve Oddish
Vileplume
Vileplume R B Y 21 Evolve Gloom
Paras
Paras R B Y 8 Walking: Mt. Moon (1F)
R B Y 9 Walking: Mt. Moon (B1F)
Parasect
Parasect R B Y 24 Evolve Paras
R B Y 22 In-Game Trade: Route 18 (trade a level 22 Tangela)
Venonat
Venonat R B Y 22 Walking: Safari Zone (Center)
R B Y 13 Walking: Routes 24 and 25
Venomoth
Venomoth R B Y 31 Evolve Venonat
R B Y 31 Walking: Safari Zone (West)
R B Y 30 Walking: Routes 14 and 15
Diglett
Diglett R B Y 15 Walking: Diglett's Cave
Dugtrio
Dugtrio R B Y 26 Evolve Diglett
Meowth
Meowth R B Y 10 Walking: Routes 5 and 6
Persian
Persian R B Y 28 Evolve Meowth
Psyduck
Psyduck R B Y 15 Fishing (Super Rod): Routes 24 and 25, Cerulean City, Safari Zone (all areas)
R B Y 15 Surfing: Route 6
Golduck
Golduck R B Y 33 Evolve Psyduck
R B Y 15 Surfing: Route 6
Mankey
Mankey R B Y 10 Walking: Routes 5 and 6
R B Y 3 Walking: Route 22
Primeape
Primeape R B Y 28 Evolve Mankey
Growlithe
Growlithe R B Y 15 Walking: Route 8
R B Y 26 Walking: Pokémon Mansion (1F)
Arcanine
Arcanine R B Y 15 Evolve Growlithe
R B Y 26 Evolve Growlithe
Poliwag
Poliwag R B Y 10 Fishing (Old Rod): Any Fishing location
R B Y 5 Fishing (Super Rod): Route 22, Viridian City
Poliwhirl
Poliwhirl R B Y 23 Fishing (Super Rod): Route 10, Celadon City
R B Y 15 Fishing (Super Rod): Route 22
Poliwrath
Poliwrath R B Y 23 Evolve Poliwhirl
R B Y 15 Evolve Poliwhirl
Abra
Abra R B Y 8 Walking: Route 24
R B Y 6 Purchase: Celadon Game Corner
R B Y 7 Walking: Routes 5 and 6
Kadabra
Kadabra R B Y 16 Evolve Abra
Alakazam
Alakazam R B Y N/A Unobtainable without trading, glitches, or events.
Machop
Machop R B Y 15 Walking: Rock Tunnel (1F and B1F)
R B Y 16 Walking: Route 10
Machoke
Machoke R B Y 28 Evolve Machop
R B Y 16 In-Game Trade: Route 5-6 Underground Path (trade a level 16 Cubone)
Machamp
Machamp R B Y 16 In-Game Trade: Route 5-6 Underground Path (trade a level 16 Cubone)
Bellsprout
Bellsprout R B Y 12 Walking: Routes 24 and 25
Weepinbell
Weepinbell R B Y 21 Evolve Bellsprout
Victreebel
Victreebel R B Y 21 Evolve Weepinbell
Tentacool
Tentacool R B Y 5 Surfing: Routes 19, 20, and 21
Fishing (Super Rod): Routes 12, 13, 17, and 18
R B Y 5 Surfing: Routes 19, 20, and 21
Fishing (Super Rod): Route 17
Tentacruel
Tentacruel R B Y 30 Evolve Tentacool
R B Y 20 Fishing (Super Rod): Route 20
Geodude
Geodude R B Y 7 Walking: Mt. Moon (B1F)
R B Y 10 Walking: Mt. Moon (1F and B1F)
Graveler
Graveler R B Y 25 Evolve Geodude
Golem
Golem R B Y N/A Unobtainable without trading, glitches, or events.
Ponyta
Ponyta R B Y 28 Walking: Pokémon Mansion (1F and 2F)
R B Y 28 Walking: Route 17
Rapidash
Rapidash R B Y 40 Evolve Ponyta
Slowpoke
Slowpoke R B Y 15 Fishing (Super Rod): Route 10, Celadon City, Safari Zone (all areas)
R B Y 15 Surfing: Routes 12 and 13
Slowbro
Slowbro R B Y 23 Fishing (Super Rod): Route 23, Cerulean Cave (1F and B1F)
R B Y 15 Surfing: Routes 12 and 13
Magnemite
Magnemite R B Y 21 Walking: Power Plant
R B Y 16 Walking: Route 10
Magneton
Magneton R B Y 30 Evolve Magnemite
Farfetch'd
Farfetch'd R B Y 3 In-Game Trade: Vermilion City (trade a level 3 Spearow)
R B Y 26 Walking: Routes 12 and 13
Doduo
Doduo R B Y 18 Walking: Route 16
R B Y 22 Walking: Routes 16 and 18
Dodrio
Dodrio R B Y 31 Evolve Doduo
R B Y 29 Walking: Route 17
Seel
Seel R B Y 28 Walking: Seafoam Islands (B1F)
R B Y 22 Walking: Seafoam Islands (B1F)
Dewgong
Dewgong R B Y 34 Evolve Seel
R B Y 26 In-Game Trade: Cinnabar Lab (trade a level 26 Growlithe)
Grimer
Grimer R B Y 30 Walking: Pokémon Mansion (1F and 2F)
R B Y 23 Walking: Pokémon Mansion (1F)
Muk
Muk R B Y 37 Walking: Pokémon Mansion (2F)
R B Y 37 Walking: Pokémon Mansion (1F)
R B Y 33 In-Game Trade: Cinnabar Lab (trade a level 22 Kangaskhan)
Shellder
Shellder R B Y 15 Fishing (Super Rod): Routes 6, 11, 19, 20, and 21, Vermilion City & Harbor, Cinnabar Island, Seafoam Islands (B3F and B4F)
R B Y 10 Fishing (Super Rod): Vermilion Harbor
Cloyster
Cloyster R B Y 15 Evolve Shellder
R B Y 10 Evolve Shellder
Gastly
Gastly R B Y 18 Walking: Pokémon Tower (3F, 4F, and 5F)
R B Y 18 Walking: Pokémon Tower (3F and 4F)
Haunter
Haunter R B Y 25 Evolve Gastly
R B Y 25 Walking: Pokémon Tower (3F, 4F, and 5F)
R B Y 20 Walking: Pokémon Tower (3F and 4F)
Gengar
Gengar R B Y N/A Unobtainable without trading, glitches, or events.
Onix
Onix R B Y 13 Walking: Rock Tunnel (1F and B1F)
R B Y 14 Walking: Rock Tunnel (B1F)
Drowzee
Drowzee R B Y 9 Walking: Route 11
R B Y 15 Walking: Route 11
Hypno
Hypno R B Y 26 Evolve Drowzee
Krabby
Krabby R B Y 15 Fishing (Super Rod): Routes 6, 11, 12, 13, 17, 18, 24, and 25, Cerulean City, Vermilion City & Harbor, Fuchsia City, and Safari Zone (all areas)
R B Y 10 Fishing (Super Rod): Route 25
Kingler
Kingler R B Y 23 Fishing (Super Rod): Route 23, Cerulean Cave (1F and B1F)
R B Y 15 Fishing (Super Rod): Route 25
Voltorb
Voltorb R B Y 14 Walking: Route 1
R B Y 33 Walking: Power Plant
Electrode
Electrode R G Y 3 In-Game Trade: Cinnabar Lab
R B Y 30 Evolve Voltorb
Exeggcute
Exeggcute R B Y 23 Walking: Safari Zone (East)
R B Y 20 Walking: Safari Zone (North)
Exeggutor
Exeggutor R B Y 23 Evolve Exeggcute
R B Y 20 Evolve Exeggcute
Cubone
Cubone R B Y 20 Walking: Pokémon Tower (3F, 4F, and 5F)
R B Y 16 Walking: Safari Zone (North)
Marowak
Marowak R B Y 28 Evolve Cubone
R B Y 24 Walking: Safari Zone (East and West)
Hitmonlee
Hitmonlee R B Y 30 Gift: Saffron City
Hitmonchan
Hitmonchan R B Y 30 Gift: Saffron City
Lickitung
Lickitung R B Y 23 In-Game Trade: Route 18 (trade a level 23 Slowbro)
R B Y 50 Walking: Cerulean Cave (B1F)
Koffing
Koffing R B Y 30 Walking: Pokémon Mansion (1F and 2F)
Weezing
Weezing R B Y 25 Evolve Koffing
Rhyhorn
Rhyhorn R B Y 25 Walking: Safari Zone (Center)
R B Y 20 Walking: Safari Zone (Center)
Rhydon
Rhydon R B Y 42 Evolve Rhyhorn
R B Y 15 In-Game Trade: Cinnabar Lab (trade a level 15 Golduck)
Chansey
Chansey R B Y 23 Walking: Safari Zone (Center)
R B Y 7 Walking: Safari Zone (Center)
Tangela
Tangela R B Y 28 Walking: Route 21
R B Y 22 Walking: Safari Zone (Center)
Kangaskhan
Kangaskhan R B Y 25 Walking: Safari Zone (East)
R B Y 22 Walking: Safari Zone (North)
Horsea
Horsea R B Y 15 Fishing (Super Rod): Routes 19, 20, and 21, Cinnabar Island, Seafoam Islands (B3F and B4F)
R B Y 5 Fishing (Super Rod): Route 11, Vermilion City
Seadra
Seadra R B Y 23 Fishing (Super Rod): Route 23, Cerulean Cave (1F and B1F)
R B Y 20 Fishing (Super Rod): Route 13
Goldeen
Goldeen R B Y 10 Fishing (Good Rod): Any Fishing location
R B Y 5 Fishing (Super Rod): Route 6, Celadon City
Seaking
Seaking R B Y 23 Fishing (Super Rod): Route 23, Fuchsia City, Cerulean Cave (1F and B1F)
R B Y 30 Fishing (Super Rod): Route 24, Cerulean City
Staryu
Staryu R B Y 15 Fishing (Super Rod): Routes 19, 20, and 21, Cinnabar Island, Seafoam Islands (B3F and B4F)
R B Y 5 Fishing (Super Rod): Pallet Town
Starmie
Starmie R B Y 15 Evolve Staryu
R B Y 5 Evolve Staryu
Mr. Mime
Mr. Mime R B Y 8 In-Game Trade: Route 2 (trade a level 8 Abra)
R B Y 6 In-Game Trade: Route 2 (trade a level 6 Abra)
R B Y 9 In-Game Trade: Route 2 (trade a level 9 Clefairy)
Scyther
Scyther R B Y 23 Walking: Safari Zone (Center)
R B Y 15 Walking: Safari Zone (East)
Jynx
Jynx R B Y 23 In-Game Trade: Cerulean City (trade a level 23 Slowbro)
Electabuzz
Electabuzz R B Y 33 Walking: Power Plant
Magmar
Magmar R B Y 34 Walking: Pokémon Mansion (3F)
Pinsir
Pinsir R B Y 20 Purchase: Celadon Game Corner
R B Y 15 Walking: Safari Zone (North)
Tauros
Tauros R B Y 26 Walking: Safari Zone (West)
R B Y 21 Walking: Safari Zone (East and West)
Magikarp
Magikarp R B Y 5 Fishing (Old Rod): Any Fishing location
Purchase: Route 4
R B Y 5 Fishing (Old Rod): Any Fishing location
Fishing (Super Rod): Fuchsia City, Safari Zone (all areas)
Purchase: Route 4
Gyarados
Gyarados R B Y 20 Evolve Magikarp
R B Y 15 Fishing (Super Rod): Fuchsia City
Lapras
Lapras R B Y 15 Gift: Silph Co.
Ditto
Ditto R B Y 23 Walking: Route 14
R B Y 12 Walking: Pokémon Mansion (B1F)
Eevee
Eevee R B Y 25 Gift: Celadon City
Vaporeon
Vaporeon R B Y 25 Evolve Eevee
Jolteon
Jolteon R B Y 25 Evolve Eevee
Flareon
Flareon R B Y 25 Evolve Eevee
Porygon
Porygon R B Y 26 Purchase: Celadon Game Corner
R B Y 18 Purchase: Celadon Game Corner
Omanyte
Omanyte R B Y 30 Gift: Cinnabar Lab
Omastar
Omastar R B Y 40 Evolve Omanyte
Kabuto
Kabuto R B Y 30 Gift: Cinnabar Lab
Kabutops
Kabutops R B Y 40 Evolve Kabuto
Aerodactyl
Aerodactyl R B Y 30 Gift: Cinnabar Lab
Snorlax
Snorlax R B Y 30 Static: Routes 12 and 16
Articuno
Articuno R B Y 50 Static: Seafoam Islands (B4F)
Zapdos
Zapdos R B Y 50 Static: Power Plant
Moltres
Moltres R B Y 50 Static: Victory Road (2F)
Dratini
Dratini R B Y 15 Fishing (Super Rod): Safari Zone (all areas)
R B Y 10 Fishing (Super Rod): Safari Zone (Center)
Dragonair
Dragonair R B Y 30 Evolve Dratini
R B Y 15 Fishing (Super Rod): Safari Zone (Center)
Dragonite
Dragonite R B Y 55 Evolve Dragonair
Mewtwo
Mewtwo R B Y 70 Static: Cerulean Cave (B1F)
Mew
Mew R B Y N/A Unobtainable without trading, glitches, or events.

The table below lists the lowest levels that each Pokémon is obtainable in all of Gen 1, allowing trading, but only with other Gen 1 games.

RBY Minimum Levels (RGBY Alone)
Pokémon Level Method of Obtaining
Parasect
Parasect 13 Catch a level 13 Venonat by walking on Route 24 or 25 in Yellow.
Trade Venonat to Red or Blue.
Complete an in-game trade in Cinnabar Lab for Tangela.
Trade Tangela to Yellow.
Complete an in-game trade in Route 18.
Dugtrio
Dugtrio 15 Catch a level 15 Slowbro by Surfing on Route 12 or 13 in Yellow.
Trade Slowbro to Red or Blue.
Complete an in-game trade on Route 18 for Lickitung.
Trade Lickitung to Yellow.
Complete an in-game trade on Route 11.
Alakazam
Alakazam 16 Trade a level 16 Kadabra evolved from an Abra from any game to any game.
Alakazam
Golem 25 Trade a level 25 Graveler evolved from a Geodude from any game to any game.
Dewgong
Dewgong 15 Catch a level 15 Growlithe by walking on Route 8 in Red.
Trade Growlithe to Yellow.
Complete an in-game trade in Cinnabar Lab.
Gengar
Gengar 20 Trade a level 20 Haunter caught by walking in Pokémon Tower 3F or 4F from Yellow to any game.
Lickitung
Lickitung 15 Catch a level 15 Slowbro by Surfing on Route 12 or 13 in Yellow.
Trade Slowbro to Red or Blue.
Complete an in-game trade on Route 18.
Tangela
Tangela 13 Catch a level 13 Venonat by walking on Route 24 or 25 in Yellow.
Trade Venonat to Red or Blue.
Complete an in-game trade in Cinnabar Lab.
Jynx
Jynx 15 Catch a level 15 Poliwhirl by fishing with a Super Rod on Route 22 inYellow.
Trade Poliwhirl to Red or Blue.
Complete an in-game trade in Cerulean City.

Pokémon Stadium

Using Pokémon Stadium, a player can get the following low-leveled Pokémon (with the game they are low-leveled in marked with parentheses):

Gold, Silver, and Crystal

The following table shows the lowest levels that can be acquired by trading Pokémon from or to Gold, Silver, or Crystal. This table contains only those Pokémon whose lowest obtainable level changes as a result of contact with Gold, Silver, or Crystal.

RGBY Minimum Levels (RGBY and GSC)
Pokémon Level Method of Obtaining
Butterfree
Butterfree 7 Catch by walking on Route 2 in Gold (Morning only) or Crystal (Morning and Day only).
Ekans
Beedrill 7 Catch by walking on Route 2 in Silver (Morning only).
Pidgeotto
Pidgeotto 7 Catch by walking on Route 2 in Gold (Morning and Day only), Silver (Day only), or Crystal (Day only).
Raticate
Raticate 6 Catch by walking on Route 1 in Crystal (Night only).
Fearow
Fearow 7 Catch by walking on Route 22 in Gold (Morning and Day only), Silver (Morning and Day only), or Crystal (Morning and Day only).
Ekans
Ekans 4 Catch by walking on Route 32 in Silver or Crystal (Morning and Day only).
Arbok
Arbok 10 Catch by walking on Route 3 or 4 in Silver or Crystal (Morning and Day only).
Sandshrew
Sandshrew 5 Breed in Gold, Silver, or Crystal.
Sandslash
Sandslash 10 Catch by walking in Mt. Moon in Gold.
Clefairy
Clefairy 6 Breed a Cleffa in Gold, Silver, or Crystal, and raise it one level with appropriate happiness to evolve it.
Catch by walking in Route 3 or 4 in Crystal (Night only).
Clefable
Clefable 6 Evolve a Clefairy obtained in Gold, Silver, or Crystal.
Vulpix
Vulpix 5 Breed in Gold, Silver, or Crystal.
Ninetales
Ninetales 5 Evolve a Vulpix bred in Gold, Silver, or Crystal.
Zubat
Zubat 2 Catch by walking in Dark Cave (Route 31/46 side) in Gold, Silver, or Crystal.
Golbat
Golbat 13 Catch by walking in Mt. Mortar (1F front) in Crystal.
Oddish
Oddish 5 Breed in Gold, Silver, or Crystal.
Catch by walking in Ilex Forest in Gold (Night only), Silver (Night only), or Crystal (Night only).
Gloom
Gloom 14 Catch by walking on Route 24 in Crystal (Night only).
Vileplume
Vileplume 14 Evolve a Gloom caught in Crystal.
Paras
Paras 5 Breed in Gold, Silver, or Crystal.
Parasect
Parasect 5 Complete an in-game trade in Cinnabar Lab in Yellow, trading a level 5 Tangela bred in Gold, Silver, or Crystal.
Venonat
Venonat 5 Breed in Gold, Silver, or Crystal.
Catch by walking in Ilex Forest in Crystal (Night only).
Venomoth
Venomoth 10 Catch by walking on Route 24 or 25 in Gold (Night only) or Silver (Night only).
Diglett
Diglett 3 Catch by walking in Diglett's Cave in Crystal (Morning only).
Dugtrio
Dugtrio 5 Complete an in-game trade on Route 11 in Yellow, trading a level 5 Lickitung bred in Gold, Silver, or Crystal.
Meowth
Meowth 5 Breed in Gold, Silver, or Crystal.
Persian
Persian 18 Catch by walking on Route 7 in Crystal (Night only).
Psyduck
Psyduck 5 Breed in Gold, Silver, or Crystal.
Catch by Surfing on Route 6 in Gold, Silver, or Crystal.
Golduck
Golduck 10 Catch by Surfing on Route 6 in Gold, Silver, or Crystal.
Primeape
Primeape 15 Catch on Route 9 in Gold.
Growlithe
Growlithe 5 Breed in Gold, Silver, or Crystal.
Catch on Route 36 in Crystal (Morning or Day only).
Arcanine
Arcanine 5 Evolve a Growlithe obtained in Gold, Silver, or Crystal.
Poliwhirl
Poliwhirl 10 Catch by Surfing in Viridian City or Route 22 in Gold, Silver, or Crystal.
Poliwrath
Poliwrath 10 Evolve a Poliwhirl caught in Gold, Silver, or Crystal.
Abra
Abra 5 Breed in Gold, Silver, or Crystal.
Purchase in the Goldenrod Game Corner in Crystal.
Kadabra
Kadabra 15 Catch on Route 8 in Gold or Silver.
Alakazam
Alakazam 15 Evolve a Kadabra caught in Gold or Silver.
Machop
Machop 5 Breed in Gold, Silver, or Crystal.
Complete an in-game trade in Goldenrod Department Store in Gold or Silver, trading a level 5 Drowzee bred in Gold, Silver, or Crystal.
Complete an in-game trade in Goldenrod Department Store in Crystal, trading a level 5 Abra obtained in Gold, Silver, or Crystal.
Machoke
Machoke 5 Complete an in-game trade in the Route 5-6 Underground Path in Yellow, trading a level 5 Cubone bred in Gold, Silver, or Crystal.
Machamp
Machamp 5 Complete an in-game trade in the Route 5-6 Underground Path in Yellow, trading a level 5 Cubone bred in Gold, Silver, or Crystal.
Bellsprout
Bellsprout 3 Catch by walking on Route 31 in Gold or Silver.
Weepinbell
Weepinbell 12 Catch by walking on Route 24 in Gold (Morning and Day only) or Silver (Morning and Day only).
Catch by walking on Route 25 in Gold or Silver.
Victreebel
Victreebel 12 Evolve a Weepinbell caught in Gold or Silver.
Geodude
Geodude 2 Catch by walking on Route 46 or Dark Cave (Route 31/46 side) in Gold, Silver, or Crystal.
Graveler
Graveler 15 Complete an in-game trade in Cinnabar Lab in Blue, trading a level 15 Kadabra caught in Gold or Silver.
Golem
Golem 15 Complete an in-game trade in Cinnabar Lab in Blue, trading a level 15 Kadabra caught in Gold or Silver.
Ponyta
Ponyta 5 Breed in Gold, Silver, or Crystal.
Rapidash
Rapidash 14 Complete an in-game trade in Pewter City in Gold or Silver, trading a level 14 Gloom caught in Crystal.
Magnemite
Magnemite 5 Breed in Gold, Silver, or Crystal.
Magneton
Magneton 5 Breed a level 5 Lickitung in Gold, Silver, or Crystal, trade it to Yellow, complete an in-game trade on Route 11 for a level 5 Dugtrio, trade the Dugtrio to Crystal, and complete an in-game trade at the Power Plant.
Doduo
Doduo 4 Catch by walking on Route 22 in Gold (Morning or Day only), Silver (Morning or Day only), or Crystal (Morning or Day only).
Dodrio
Dodrio 10 Complete an in-game trade in Blackthorn City in Crystal, trading a level 10 female Dragonair caught in Gold, Silver, or Crystal.
Seel
Seel 5 Breed in Gold, Silver, or Crystal.
Dewgong
Dewgong 5 Complete an in-game trade in Cinnabar Lab in Yellow, trading a Growlithe obtained in Gold, Silver, or Crystal.
Grimer
Grimer 5 Breed in Gold, Silver, or Crystal.
Muk
Muk 5 Complete an in-game trade in Cinnabar Lab in Yellow, trading a level 5 Kangaskhan bred in Gold, Silver, or Crystal.
Shellder
Shellder 5 Breed in Gold, Silver, or Crystal.
Cloyster
Cloyster 5 Evolve a Shellder bred in Gold, Silver, or Crystal.
Gastly
Gastly 3 Catch by walking in Sprout Tower (2F and 3F) in Gold (Night only), Silver (Night only), or Crystal (Night only).
Haunter
Haunter 15 Catch by walking in Rock Tunnel (B1F) in Crystal (Night only).
Gengar
Gengar 15 Evolve a Haunter caught in Crystal.
Onix
Onix 3 Complete an in-game trade in Violet City in Gold, Silver, or Crystal, trading a level 3 Bellsprout caught in Gold or Silver.
Drowzee
Drowzee 5 Breed in Gold, Silver, or Crystal.
Hypno
Hypno 16 Catch by walking on Route 11 in Gold, Silver, or Crystal (Night only).
Krabby
Krabby 5 Breed in Gold, Silver, or Crystal.
Voltorb
Voltorb 5 Breed in Gold, Silver, or Crystal.
Complete an in-game trade in Olivine City in Gold, Silver, or Crystal, trading a level 5 Krabby bred in Gold, Silver, or Crystal.
Exeggcute
Exeggcute 5 Breed in Gold, Silver, or Crystal.
Exeggutor
Exeggutor 5 Evolve an Exeggcute bred in Gold, Silver, or Crystal.
Cubone
Cubone 5 Breed in Gold, Silver, or Crystal.
Marowak
Marowak 12 Catch by walking in Rock Tunnel (1F) in Crystal (Morning and Day only).
Lickitung
Lickitung 5 Breed in Gold, Silver, or Crystal.
Koffing
Koffing 5 Breed in Gold, Silver, or Crystal.
Weezing
Weezing 16 Catch by walking in Burned Tower (B1F) in Crystal.
Rhyhorn
Rhyhorn 5 Breed in Gold, Silver, or Crystal.
Rhydon
Rhydon 10 Complete an in-game trade in Cinnabar Lab in Yellow, trading a level 10 Golduck caught in Gold, Silver, or Crystal.
Complete an in-game trade in Blackthorn City in Gold or Silver, trading a level 10 female Dragonair caught in Gold, Silver, or Crystal.
Chansey
Chansey 5 Breed in Gold, Silver, or Crystal.
Tangela
Tangela 5 Breed in Gold, Silver, or Crystal.
Kangaskhan
Kangaskhan 5 Breed in Gold, Silver, or Crystal.
Seaking
Seaking 10 Catch by Surfing on Route 4, 24, or 25, or Cerulean City in Gold, Silver, or Crystal.
Scyther
Scyther 5 Breed in Gold, Silver, or Crystal.
Jynx
Jynx 10 Complete an in-game trade in Cerulean City in Red or Green (Western Blue), trading a level 10 Poliwhirl caught in Gold, Silver, or Crystal.
Electabuzz
Electabuzz 15 Catch by walking on Route 15 in Gold or Silver.
Magmar
Magmar 14 Catch by walking in Burned Tower (B1F) in Gold (Morning or Night only) or Silver (Morning or Night only).
Pinsir
Pinsir 5 Breed in Gold, Silver, or Crystal.
Tauros
Tauros 5 Breed in Gold, Silver, or Crystal.
Lapras
Lapras 5 Breed in Gold, Silver, or Crystal.
Ditto
Ditto 10 Catch on Route 34 or 35 in Gold, Silver, or Crystal.
Eevee
Eevee 5 Breed in Gold, Silver, or Crystal.
Vaporeon
Vaporeon 5 Evolve an Eevee bred in Gold, Silver, or Crystal.
Jolteon
Jolteon 5 Evolve an Eevee bred in Gold, Silver, or Crystal.
Flareon
Flareon 5 Evolve an Eevee bred in Gold, Silver, or Crystal.
Porygon
Porygon 5 Breed in Gold, Silver, or Crystal.
Omanyte
Omanyte 5 Breed in Gold, Silver, or Crystal.
Kabuto
Kabuto 5 Breed in Gold, Silver, or Crystal.
Aerodactyl
Aerodactyl 5 Breed in Gold, Silver, or Crystal.
Complete an in-game trade on Route 14 in Gold, Silver, or Crystal, trading a level 5 Chansey bred in Gold, Silver, or Crystal.
Snorlax
Snorlax 5 Breed in Gold, Silver, or Crystal.
Dratini
Dratini 5 Breed in Gold, Silver, or Crystal.
Dragonair
Dragonair 10 Catch by Fishing with a Super Rod on Route 45 in Gold, Silver, or Crystal.

Events

Mew was distributed in Japan, Australia, the USA, Canada, the UK, the Republic of Ireland, Spain, France, Germany, and Belgium to Red, Green, Blue, and Yellow in various events held between 1996 and 2000.
Mew was distributed in the USA to Gold, Silver, and Crystal in an event held in November 2002.
Mew was distributed in Japan and the UK to virtual console copies of Red, Green, Blue, and Yellow in events held in 2016.
The lowest level possible for one of the Mew distributions was level 5.

Several Pokémon were also distributed at level 5 to Gold, Silver, and Crystal. All such Pokémon can be found at level 5 already in one or more games, so I have not listed them, as the events are long gone.

Glitches

The Mew glitch can be used with the enemy Ditto method to obtain all Gen 1 Pokémon at level 7.
Using Growl up to 6 times during the battle against the Pokémon whose Special stat is used to generate a Pokémon will lower the encountered Pokémon's level by 1 for each use, to a minimum of 1. Therefore, it is possible to get any Pokémon at level 1.