How Many Pokémon Can You Get with Only Pokémon Blue (Japanese)?
Assuming you do not use any glitches, the answer is 126. As of this writing, a Professor Oak Challenge guide for this game is not yet written, but I've provided rough notes at the bottom of this page.
The list of Pokémon you cannot get without trading, which equals 25 species, is as follows:
- Two Starters (6) - 6 total
- As you can only select one starter Pokémon, the other two starters, and their evolutions, are unavailable; this totals 6 Pokémon.
- Trade Evolutions (2) - 8 total
- Machamp and Alakazam evolve by trade. Without the ability to trade, they are unobtainable. You can get Golem and Gengar via in-game trade.
- Two Eeveelutions (2) - 10 total
- As you only receive one Eevee, you can only receive one of its evolutions.
- One Fossil (2) - 12 total
- As you can only obtain one Fossil in Mt. Moon, you miss out on the other Fossil Pokémon and its evolution.
- One Hitmon (1) - 13 total
- As you can only obtain one Hitmon, you miss out on the other.
- Version Exclusives (11) - 24 total
- The following Pokémon, and their evolutions, cannot be obtained without the use of glitches or trading: Ekans, Vulpix, Mankey, Bellsprout, Electabuzz, Magmar.
- Mythical/Event (1) - 25 total
- Outside of glitches, Mew was only obtainable via events that are no longer active. However, Mew was never needed to get the certificate from the Game Freak employee.
Professor Oak Challenge Notes
Pre-Badge 1 (Brock)
- Pallet Town: One starter & Evolutions (3 total)
- Route 1: Pidgey, Pidgeotto, Pidgeot (6 total)
- Route 1: Rattata, Raticate (8 total)
- Route 22: Nidoran♂, Nidorino (10 total)
- Route 22: Nidoran♀, Nidorina (12 total)
- Route 22: Spearow, Fearow (14 total)
- Viridian Forest: Caterpie, Metapod, Butterfree (17 total)
- Viridian Forest: Weedle, Kakuna, Beedrill (20 total)
- Viridian Forest: Pikachu (21 total)
Badge 1 through Badge 2 (Misty)
- Route 3: Jigglypuff (22 total)
- Route 3: Sandshrew, Sandslash (24 total)
- Route 4: Magikarp, Gyarados (26 total)
- Mt. Moon: Zubat, Golbat (28 total)
- Mt. Moon: Paras, Parasect (30 total)
- Mt. Moon: Geodude, Graveler (32 total)
- Mt. Moon: Clefairy (33 total)
- Route 24: Oddish, Gloom (35 total)
- Route 24: Abra, Kadabra (37 total)
- Route 5: Meowth, Persian (39 total)
- Underground Path House: Poliwag (& Poliwhirl): Trade Your Rattata (41 total)
- Vermilion City: Farfetch'd: Trade Your Pidgey (42 total)
- Route 11: Drowzee, Hypno (44 total)
- Diglett's Cave: Diglett, Dugtrio (46 total)
- Route 2: Mr. Mime: Trade Your Jigglypuff (47 total)
- Evolve Two Moon Stone Pokémon with Moon Stones from Mt. Moon (49 total)
Badge 2 through Badge 3 (Koga)
- Route 10: Voltorb, Electrode (51 total)
- Rock Tunnel: Machop, Machoke (53 total)
- Rock Tunnel: Onix (54 total)
- Rock Tunnel: Ditto (55 total)
- Cerulean City: Haunter (& Gengar): Trade Your Machoke (57 total)
- Route 8: Growlithe (58 total)
- Celadon City: Eevee & 1 Evolution (60 total)
- Celadon Game Corner: Porygon (61 total)
- Buy a Thunderstone: Evolve Pikachu (62 total)
- Buy a Fire Stone: Evolve Growlithe (63 total)
- Buy a Leaf Stone: Evolve Gloom (64 total)
- Buy a Water Stone: Evolve Poliwhirl (65 total)
- Evolve Two Moon Stone Pokémon with Moon Stones from Rocket Hideout and Route 2 (67 total) (alternatively, purchase a Clefable at Celadon Game Corner)
- Route 16: Doduo, Dodrio (69 total)
- Pokémon Tower: Gastly (70 total)
- Pokémon Tower: Cubone, Marowak (72 total)
- Route 16/12: Snorlax (73 total)
- Super Rod in Vermilion City: Shellder, Cloyster (75 total)
- Good Rod in Vermilion City: Goldeen, Seaking (77 total)
- Super Rod in Vermilion City: Krabby, Kingler (79 total)
- Super Rod on Route 19: Horsea, Seadra (81 total)
- Super Rod on Route 19: Staryu, Starmie (83 total)
- Super Rod on Route 24: Psyduck, Golduck (85 total)
- Super Rod on Route 10: Slowpoke, Slowbro (87 total)
- Super Rod in Viridian City: Tentacool, Tentacruel (89 total)
- Route 15: Venonat, Venomoth (91 total)
- Safari Zone: Rhyhorn, Rhydon (93 total)
- Safari Zone: Exeggcute, Exeggutor (95 total)
- Safari Zone: Scyther (96 total)
- Safari Zone: Chansey (97 total)
- Safari Zone: Lickitung (98 total)
- Safari Zone: Pinsir (99 total)
- Super Rod in Safari Zone: Dratini, Dragonair, Dragonite (102 total)
- Route 18: Tauros: Trade Your Persian (103 total)
- Route 11: Kangaskhan: Trade Your Rhydon (104 total)
- Saffron City: One Hitmon (105 total)
- Silph Co.: Lapras (106 total)
Badge 3 through Badge 4 (Erika)
- Power Plant: Magnemite, Magneton (108 total)
- Power Plant: Zapdos (109 total)
- Cinnabar Lab: Aerodactyl (110 total)
- Cinnabar Lab: Fossil & Evolution (112 total)
- Pokémon Mansion: Grimer, Muk (114 total)
- Pokémon Mansion: Ponyta, Rapidash (116 total)
- Pokémon Mansion: Koffing, Weezing (118 total)
- Seafoam Islands (B2F): Jynx (119 total)
- Seafoam Islands: Seel, Dewgong (121 total)
- Cinnabar Lab: Golem: Trade Your Kadabra (122 total)
- Route 21: Tangela (123 total)
Badges 4 through 8
- Seafoam Islands: Articuno (124 total)
Badge 8 through Elite Four
- Victory Road: Moltres (125 total)
Post-Elite Four
- Cerulean Cave: Mewtwo (126 total)