How Many Pokémon Can You Get with Only Pokémon Crystal?
Assuming you do not use any glitches, the answer is 207 if you are using the Virtual Console release of Crystal (allowing access to Celebi), or 206 otherwise. The Professor Oak challenge guide for Crystal can be found here, although I've made a shorter list of encounters below in case anything happens to the external guide.
The list of Pokémon you cannot get without trading, which equals 44 or 45 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.
- Kanto Starters (9) - 15 total
- None of the Kanto starters can be obtained without trading with Gen 1 games.
- Kanto Legendaries (4) - 19 total
- Articuno, Zapdos, Moltres, and Mewtwo are unobtainable without trading with Gen 1 games.
- Kanto Fossils (4) - 23 total
- Omanyte, Omastar, Kabuto, and Kabutops are unobtainable without trading with Gen 1 games.
- Trade Evolutions (10) - 33 total
- Golem, Machamp, Alakazam, Gengar, Politoed, Slowking, Steelix, Scizor, Kingdra, and Porygon2 evolve by trade. Without the ability to trade, they are unobtainable.
- Version Exclusives (10) - 43 total
- The following Pokémon, and their evolutions, cannot be obtained without the use of glitches or trading: Mareep, Vulpix, Mankey, Girafarig, and Remoraid.
- Mythical/Event (1/2) - 44 or 45 total
- Outside of glitches, Mew was only obtainable via events that are no longer active. Celebi can be obtained in the Virtual Console release of Crystal, but not on the original cartridge release. However, they were never needed to get the certificate from the Game Freak employee.
Professor Oak Challenge Notes
Pre-Badge 1 (Falkner)
- New Bark Town: One starter & evolutions (3 total)
- Route 29: Pidgey, Pidgeotto, Pidgeot (6 total)
- Route 29: Hoppip, Skiploom, Jumpluff (9 total)
- Route 29: Sentret, Furret (11 total)
- Route 29: Hoothoot, Noctowl (13 total)
- Route 29: Rattata, Raticate (15 total)
- Route 46: Phanpy, Donphan (17 total)
- Route 46: Geodude, Graveler (19 total)
- Route 46: Spearow, Fearow (21 total)
- Route 30: Caterpie, Metapod, Butterfree (24 total)
- Route 30: Weedle, Kakuna, Beedrill (27 total)
- Route 30: Spinarak, Ariados (29 total)
- Route 30: Ledyba, Ledian (31 total)
- Route 30: Zubat, Golbat, Crobat (34 total)
- Route 30: Poliwag, Poliwhirl (36 total)
- Route 31: Bellsprout, Weepinbell (38 total)
- Route 31: Gastly, Haunter (40 total)
- Dark Cave: Dunsparce (41 total)
- Dark Cave: Teddiursa, Ursaring (43 total)
- Violet City: Onix: Trade Your Bellsprout (44 total)
- Route 36: Growlithe (45 total)
- Ruins of Alph: Unown (46 total)
Badge 1 through Badge 2 (Bugsy)
- Violet City Egg: Togepi, Togetic (48 total)
- Route 32: Wooper, Quagsire (50 total)
- Route 32: Ekans, Arbok (52 total)
- Old Rod Anywhere: Magikarp, Gyarados (54 total)
- Old Rod in New Bark Town: Tentacool, Tentacruel (56 total)
- Old Rod in Cherrygrove City: Krabby, Kingler (58 total)
- Old Rod in Dark Cave: Goldeen, Seaking (60 total)
- Old Rod on Route 32: Qwilfish (61 total)
- Union Cave: Sandshrew, Sandslash (63 total)
- Slowpoke Well: Slowpoke, Slowbro (65 total)
- Ilex Forest: Oddish, Gloom (67 total)
- Ilex Forest: Paras, Parasect (69 total)
- Ilex Forest: Psyduck, Golduck (71 total)
- Ilex Forest: Venonat, Venomoth (73 total)
- Headbutt in Ilex Forest: Exeggcute (74 total) - you will need to level up Slowpoke to get Headbutt
- Headbutt in Ilex Forest: Pineco, Forretress (76 total) - you will need to level up Slowpoke to get Headbutt
- Headbutt on Route 33: Aipom (77 total) - you will need to level up Slowpoke to get Headbutt
- Headbutt on Route 33: Heracross (78 total) - you will need to level up Slowpoke to get Headbutt
Badge 2 through Badge 3 (Whitney)
- Route 34: Drowzee, Hypno (80 total)
- Route 34: Abra, Kadabra (82 total)
- Route 34: Ditto (83 total)
- Route 34: Snubbull, Granbull (85 total)
- Route 34: Jigglypuff (86 total)
- Route 34: Igglybuff: Breed Your Jigglypuff (87 total)
- Route 34: Odd Egg: Tyrogue, Hitmontop (89 total)
- Route 34: Hitmonchan: Breed Your Hitmontop (90 total)
- Route 34: Hitmonlee: Breed Your Hitmontop (91 total)
- Goldenrod City: Machop (& Machoke): Trade Your Drowzee (93 total)
- Goldenrod Game Corner: Cubone, Marowak (95 total)
- Goldenrod Game Corner: Wobbuffet (96 total)
- Route 35: Yanma (97 total)
- National Park: Nidoran♀, Nidorina (99 total)
- National Park: Nidoran♂, Nidorino (101 total)
- National Park: Sunkern (102 total)
- Bug-Catching Contest: Scyther (103 total)
- Bug-Catching Contest: Pinsir (104 total)
- Win the Bug-Catching Contest for a Sun Stone: Evolve Gloom (105 total)
- Win the Bug-Catching Contest for a Sun Stone: Evolve Sunkern (106 total)
- Evolve One Moon Stone Pokémon with the Moon Stone Purchased by Your Mother (107 total)
- Evolve Exeggcute, Gloom, and Weepinbell with Leaf Stones from Picnicker Gina (110 total)
- Evolve Growlithe with a Fire Stone from Schoolboy Alan (111 total)
Badge 3 through Badge 4 (Morty)
- Route 36: Sudowoodo (112 total)
- Route 37: Stantler (113 total)
- Goldenrod City: Eevee, Espeon (115 total) - talk to Bill in Ecruteak first
- Route 34: Umbreon: Breed Your Espeon (116 total)
- Route 34: Flareon: Breed Your Espeon & Evolve with a Fire Stone from Schoolboy Alan (117 total)
- Burned Tower: Koffing, Weezing (119 total)
- Route 38: Magnemite, Magneton (121 total)
- Route 38: Miltank (122 total)
- Route 38: Tauros (123 total)
- Route 39: Meowth, Persian (125 total)
- Route 34: Jolteon: Breed Your Espeon & Evolve with a Thunderstone from Lass Dana (126 total)
- Rock Smash on Route 40: Shuckle (127 total)
- Olivine City: Voltorb (& Electrode): Trade Your Krabby (129 total)
- Good Rod in Olivine Harbor: Shellder (130 total)
- Good Rod in Olivine Harbor: Chinchou, Lanturn (132 total)
- Good Rod in Olivine City: Corsola (133 total)
- Good Rod in Olivine City: Staryu (134 total)
- Mt. Mortar: Marill, Azumarill (136 total)
- Evolve Shellder, Staryu, Eevee, and Poliwhirl with Water Stones from Fisher Tully (140 total)
- Route 43: Farfetch'd (141 total)
- Roaming: Entei, Raikou (143 total)
Badge 4 through Badge 5 (Pryce)
- Evolve Two Moon Stone Pokémon with Moon Stones from Tohjo Falls and Ruins of Alph (145 total)
- Ruins of Alph: Natu, Xatu (147 total)
- Ruins of Alph: Smeargle (148 total)
- Union Cave: Lapras (149 total)
- Route 41: Mantine (150 total)
Badges 5 through 7 (Jasmine or Chuck)
- Whirl Islands: Seel, Dewgong (152 total)
- Whirl Islands: Horsea, Seadra (154 total)
Badge 7 through 8 (Clair)
- Tin Tower: Suicune (155 total)
- Route 44: Lickitung (156 total)
- Route 44: Tangela (157 total)
- Ice Path: Jynx (158 total)
- Route 34: Smoochum: Breed Your Jynx (159 total)
- Ice Path: Swinub, Piloswine (161 total)
- Ice Path: Delibird (162 total)
- Ice Path: Sneasel (163 total)
- Fishing on Route 45: Dratini, Dragonair, Dragonite (166 total)
- Blackthorn City: Dodrio: Trade Your Dragonair (167 total)
- Route 34: Doduo: Breed Your Dodrio (168 total)
- Route 45: Gligar (169 total)
- Route 45: Skarmory (170 total)
Badge 8 through Elite Four
- Route 27: Ponyta, Rapidash (172 total)
- Victory Road: Rhyhorn, Rhydon (174 total)
Elite Four through Kanto Badge 1
- Ilex Forest: Virtual Console Celebi (175 total)
- Route 10: Electabuzz (176 total)
- Route 34: Elekid: Breed Your Electabuzz (177 total)
- Rock Tunnel: Kangaskhan (178 total)
- Route 7: Houndour, Houndoom (180 total)
- Route 7: Murkrow (181 total)
- Celadon Game Corner: Porygon (182 total)
- Celadon Game Corner: Larvitar, Pupitar, Tyranitar (185 total)
- Surfing in Celadon City: Grimer, Muk (187 total)
- Route 16: Slugma, Magcargo (189 total)
- Route 15: Chansey, Blissey (191 total)
- Route 14: Aerodactyl: Trade Your Chansey (192 total)
- Vermilion City: Snorlax (193 total)
- Diglett's Cave: Diglett, Dugtrio (195 total)
- Route 2: Pikachu, Raichu (197 total)
- Route 34: Pichu: Breed Your Pikachu (198 total)
- Route 21: Mr. Mime (199 total)
- Mt. Moon: Clefairy, Clefable (201 total)
- Route 34: Cleffa: Breed Your Clefairy (202 total)
- Tin Tower: Ho-Oh (203 total)
- Whirl Islands: Lugia (204 total)
Post-Kanto Badges
- Mt. Silver: Misdreavus (205 total)
- Mt. Silver: Magmar (206 total)
- Route 34: Breed Your Magmar (207 total, or 206 without Virtual Console Celebi)