I had mostly every Pokemon possible in my Blue version, even Mew... but since I had no extra Gameboy I had no way of obtaining the following:
Red Exclusives:
[icon]023[/icon] [icon]024[/icon] [icon]043[/icon] [icon]044[/icon] [icon]045[/icon] [icon]056[/icon] [icon]057[/icon] [icon]058[/icon] [icon]059[/icon] [icon]123[/icon] [icon]125[/icon]
Choice Events:
[icon]001[/icon] [icon]002[/icon] [icon]003[/icon]: I picked Squirtle... but Venusaur is the BEST starter in this game... PERIOD. But that Poison typing is such a curse >.<
[icon]004[/icon] [icon]005[/icon] [icon]006[/icon]: See above... Charizard is decent but still not good enough in my opinion. It had a base Special Attack and Special Defense of 85 in this game... and that's bad!
[icon]106[/icon]: Yes, I picked Hitmonchan over this one. Neither of them are good but Lee is MUCH better than Chan, even today. >.>
[icon]135[/icon] [icon]136[/icon]: I evolved Eevee into a Vaporeon instead of the other two. Why? Simply because I love it the best. Vaporeon is good... Jolteon is all right, but Flareon fails. My favorite is Vaporeon... Flareon comes second, and Jolteon comes third. Argh, Flareon's failitude started even way back here!
[icon]140[/icon] [icon]141[/icon]: I picked Omanyte because he is obviously the better one but everyone knows Kabutops looks cooler
Trade Pokemon: I could not obtain these for they must be TRADED to evolve. Note that in Yellow it is possible to obtain Machamp without other Gameboy interaction via trading a Cubone for a Machoke in the Underground Path entrance at Route 5 (below Cerulean).
[icon]065[/icon]: Trade Kadabra to get Alakazam. Possibly the best non-uber in game
[icon]068[/icon]: Trade Machoke to get Machamp. If you were a fighter back then it meant suicide
[icon]076[/icon]: Trade Graveler to get Golem. Golem is just another Rhydon but it can blow up... use Rhydon instead
[icon]094[/icon]: Trade Haunter to get Gengar. It is a weaker Alakazam with a different typing and a weakness to Earthquake... > The ginormous movepool is helpful though. Ironically, this is the Pokemon built to stop Alakazam... or is it? Its stats scream "Alakazam will own me!"
Since that is a total deficit of 25 Pokemon, I had 126 Pokemon in total (yes I had Mew as well via the Mew glitch). The hardest to get in my opinion was Rapidash... I mean this trick pony that only knows Ember and Tail Whip... to train it up to level 40 to evolve? That is insane!
For those who have Red version and want to know which Pokemon are unattainable in Red version (aka Blue exclusives):
[icon]027[/icon] [icon]028[/icon] [icon]037[/icon] [icon]038[/icon] [icon]052[/icon] [icon]053[/icon] [icon]069[/icon] [icon]070[/icon] [icon]071[/icon] [icon]126[/icon] [icon]127[/icon]
Pokemon unattainable in Yellow version:
[icon]013[/icon] [icon]014[/icon] [icon]015[/icon] [icon]023[/icon] [icon]024[/icon] [icon]026[/icon] [icon]052[/icon] [icon]053[/icon] [icon]109[/icon] [icon]110[/icon] [icon]124[/icon] [icon]125[/icon] [icon]126[/icon]
The reasoning behind Weedle is because Ash failed to catch it in the anime... but by that logic, Spearow should be unavailable too. Pikachu refuses to evolve and that is the only Pikachu you get in-game. As for the others, they are either Team Rocket's Pokemon or they are the three great elementals, only one you will actually see (Jynx from Lorieli)
Wondering about [icon]123[/icon] and [icon]127[/icon]? They are available at the Game Corner for ~ 6500 coins each (I believe).
Some people think there are more unattainable Pokemon, but the simple fact is, some Pokemon are a lot more rare in one version than in the other, and vice versa. Here is a list of some that you might have trouble finding:
[icon]010[/icon] [icon]011[/icon] [icon]012[/icon]: Caterpie and Metapod are more common in Blue than in Red
Counterpart: Weedle family
[icon]013[/icon] [icon]014[/icon] [icon]015[/icon]: Weedle and Kakuna are more common in Red than in Blue
Counterpart: Caterpie family
[icon]026[/icon]: Although a non-issue, there are Raichus available in the wild exclusive to Blue in the Power Plant. But you can easily catch the rare Pikachu in Power Plant and Viridian Forest and use a Thunderstone which you can buy at Celadon Department Store for 2100. Besides, they are also available in the Unknown Dungeon in both versions.
[icon]029[/icon] [icon]030[/icon] [icon]031[/icon]: The Female Nidorans and Nidorinas are more common in Blue than in Red
Counterpart: Male Nidoran family
[icon]032[/icon] [icon]033[/icon] [icon]034[/icon]: The Male Nidorans and Nidorinos are more common in Red than in Blue
Counterpart: Female Nidoran family
[icon]088[/icon] [icon]089[/icon]: Grimer and the rare Muk are more common in Blue than in Red
Counterpart: Koffing family
[icon]098[/icon] [icon]099[/icon]: Krabby and the rare Kingler are more common in Blue than in Red
Counterpart: Horsea family
[icon]109[/icon] [icon]110[/icon]: Koffing and the rare Weezing are more common in Red than in Blue
Counterpart: Grimer family
[icon]116[/icon] [icon]117[/icon]: Horsea and the rare Seadra are more common in Red than in Blue
Counterpart: Krabby family
Event Pokemons:
[icon]001[/icon] [icon]004[/icon] [icon]007[/icon]: In the beginning you get a choice among these three. Honestly just pick Bulbasaur if you want to win or just pick whoever is your favorite... Charmander will make your game difficult though. In Yellow you get to grab all three! But that is much later in the game. BTW Charizard could not learn Fly until Yellow version came out. Bulbasaur is in the same place you get Jynx (see below), Charmander is given by the man at the top of Nugget Bridge in Route 24 (at the ledge) and Squirtle is given by Officer Jenny in Vermilion after you beat Lt. Surge. They are all level 10.
[icon]025[/icon]: Yellow only... it is your starter and it refuses to evolve. This was BEFORE the Light Ball was invented... FAIL! In Red and Blue just grab one at Viridian Forest (albeit rare) or one at the Power Plant. Or just grab a Raichu... who only has Thundershock and Growl and Thunder Wave... but TMs solve the problem there. Oh and Pikachu started learning Thunderbolt naturally at Yellow at level 26... too bad it could not in the other two.
[icon]068[/icon]: In Yellow there actually is a way to get Machamp in game. In the Underground entrance in Route 5 (below Cerulean) there is a girl who will trade you a Machoke for your Cubone (in the other two versions she offers a Female Nidoran named Spot for a Male Nidoran... lame considering there is another guy offering a Nidorina named Terry for a Nidorino >.>). Once you trade, the game will think you traded (duh!) so Machoke will evolve into Machamp. His name is Ricky. You can trade a level 5 Cubone from GSC and gain a level 5 Machamp this way too! But with such a limited move list with Karate Chop/Low Kick/Leer/Focus Energy/Seismic Toss/Submission... is it really needed in RBY other than to complete your Pokedex?
[icon]083[/icon]: In Red and Blue the house near the Mart (to the left) has a girl who is willing to trade her Farfetch'd named Dux for a common Spearow. Poor Farfy has been ruined since this generation and they refused to improve it. In Yellow they are available in the wild in Silence Bridge (Route 12-13, the place with epic music). You will need Cut to access the grass.
[icon]106[/icon] [icon]107[/icon]: This is your reward for beating the Fighting Dojo. Unlike in the later generations these two only had 35 Special Defense... and that automatically means they fail since they are weak to Psychic. Plus Hitmonchan could learn all three elemental punches... but with 35 Special Attack... that fails. Just grab Hitmonlee who is better than Hitmonchan but none of them are that great. So what about the posters behind each of them? Behind lee says "Enemies on every side!" while chan's states "What goes around comes around".
[icon]108[/icon]: In Red and Blue go to the gatehouse to the west of Celadon and go upstairs (I believe this is the location, but it is in the upstairs of some gatehouse). The guy will ask you for a Slowbro if you want his Lickitung named Marc (I think... I forgot). Lickitung is a bad Snorlax who cannot blow up (ironically now it can and gets the strongest Explosion) >.< In Yellow they are all over Unknown Dungeon.
[icon]122[/icon]: I think it is in all three versions. You'll need Cut or access Vermilion City's Diglett Cave to get to the other side of Route 2. In a house, a man will trade you his Mr. Mime named Marcel for an Abra. I believe in Yellow you trade a Clefairy for a Mr. Mime.
[icon]124[/icon]: In Red and Blue, you can trade a Poliwhirl for a Jynx in the house to the left of the Pokemon Center. In Yellow if Pikachu is happy enough you get a Bulbasaur ^^
[icon]129[/icon]: That man in the Pokemon Center near Mt. Moon sells it for 500. Get it if you want an early Gyarados... otherwise, just say no to an old pedophile and wait until Vermilion to get an Old Rod from the Fishing Guru (left house of the Pokemon Center), which gives you 100% chance to capture level 5 Magikarps anyhow... so yeah, that man rips you off. But I always get it just because I want an early Gyarados... considering there are NO wild Gyarados in this game, and the only Gyarados you see is Lance's (or your rival's in Red and Blue if your starter isn't Charmander)
[icon]131[/icon]: It is easy to get this thing actually. In Silph Co. after you fight your rival (get key at 5th floor... teleporter near the bottom leads you to the place... get to 3rd floor and use the Card Key on your first left barricade and take the teleporter there), talk to the guy below your rival after you whoop him and claim your prize. Lapras is level 15 when you get her and she is a good Pokemon to teach HM03 Surf to. She is level 20 in FRLG.
[icon]133[/icon]: It was supposed to be your starter in Yellow but you got stuck with that idiot Pikachu!!! WHY?!!! Anyhow go to Celadon City and go BEHIND the Pokemon Center and go left until you see a GIANT building. Now go in, and get to the top level and inside that mini house on the roof you will find a Pokeball containing a level 25 Eevee.
[icon]137[/icon]: It is a prize at the Game Corner... only 9999 coins in Red and Yellow and the subsequent generations. Okay yeah, that's ALL your coins... and it definitely is not worth it. In Blue it is 6000 coins but at a lower level. So take your pick... either way, it isn't that great.
[icon]138[/icon] [icon]140[/icon]: At the end of Mt. Moon that Super Nerd will challenge you. If you beat him (and you must) you get a choice between Helix and Dome fossil. Helix will get you Omanyte (looks like an Ammonite) while Dome will get you a Kabutops (looks like a Trilobite). Once you hit Cinnibar you can head to the lab to revive it. You get a choice of ONE. Honestly pick Omanyte, but both are not so great... but Omanyte is rather powerful and great defensively but that typing is a letdown. But Surf and Blizzard from 115 Special and that 125 Defense is rather great. Kabuto on the other hand... has no real physical attacks to take advantage of. Yikes! Both of them will be level 30... and they evolve at level 40. In FRLG they are both level 5.
[icon]142[/icon]: In the Museum pay 50 and look at that old skeleton. That's Aerodactyl. Just kidding... you cannot even obtain that thing because it's long dead! You need Cut and get to the other entrance at Pewter's Museum. One of the scientists will give you an Old Amber. Now go to Cinnibar and revive it... and it will be level 30 with a 35 BP Wing Attack and Agility to raise its already high speed even more. Whoo hoo... and it learns Hyper Beam at level 54. In FRLG they are both level 5.
[icon]143[/icon]: You need the Poke Flute to wake these lugs up. You have two chances to get it... one is at Route 12 the other is at Route 16. They are both level 30.
Other Rarities:
[icon]012[/icon]: They're not available in the wild, so get that Caterpie to evolve to a Metapod at level 7 and get it to become a Butterfree at level 10. No do not use a wild Metapod, because it will be stuck at Harden even as a Butterfree for some dumb reason X_X
[icon]015[/icon]: Same deal here... get a Weedle and evolve it to Kakuna at level 7 and evolve it into Beedrill at level 10. Yes, this involves ACTUAL training (gasp!)
[icon]018[/icon]: You can find Pidgeys and Pidgeottos EVERYWHERE. It evolves into Pidgeot at level 36 though >.<
[icon]026[/icon]: Raichus are available in the wild at the Unknown Dungeon and in Blue, the Power Plant. Alternately, just buy a Thunderstone for 2100 and evolve that Pikachu you found at Viridian Forest/Power Plant.
[icon]031[/icon]: Nidoran Females evolve at level 16... then use that Moon Stone on it. Try evolving it before level 23. It learns Body Slam as a Nidoqueen ONLY at level 23. The Nidos are found on that route to the west of Viridian City or in Safari Zone (Yellow has them in that route between Cerulean and Rock Tunnel as well).
[icon]034[/icon]: Same deal here... only it learns Thrash at level 23. Moon Stone the Nidorino once you get it at level 16 (or Safari Zone). The Nidos are found on that route to the west of Viridian City or in Safari Zone (Yellow has them in that route between Cerulean and Rock Tunnel as well).
[icon]036[/icon]: Clefairies are only found in Mt. Moon and are quite rare. The ONLY way to get a Clefable is to Moon Stone it. Too bad it does not learn anything as a Clefable. Clefable is not so great in this game anyways.
[icon]038[/icon]: This foxy vixen is only attained by getting a Vulpix and using the Fire Stone purchasable for 2100 at Celadon Department Store. Try evolving it at level 35 when it learns Flamethrower as a Vulpix. If you do not care for her, just evolve it for the sake of Pokedex completion.
[icon]040[/icon]: Wigglytuff is another Moon Stoner... evolve Jigglypuff with a Moon Stone... and not learn anything. But you can get one in Unknown Dungeon in Red and Blue... those things are CREEPY! They have Down's Syndrome and will use Disable... but are utterly useless >.<
I know Moon Stones are rare... and I have only found FOUR in the entire game (two in Mt. Moon, one hidden near the end, other visible, other in the other side of Route 2, and the other in the Game Corner Rocket base) so use them only if you want to. Otherwise, you can catch a wild Wigglytuff and end up managing to save one while you evolve the other three Pokemon.
[icon]045[/icon]: Evolve Gloom with a Leaf Stone.
[icon]054[/icon] [icon]055[/icon]: In Yellow they are ONLY available in that lake in Route 8 (above Vermilion). You might even find wild Golducks there if you're lucky. In the other two versions they are more common.
[icon]059[/icon]: Fire Stone that Growlithe... and not learn anything >.<
[icon]060[/icon] [icon]061[/icon] [icon]062[/icon]: Get a Good Rod at Fuschia to fish out Poliwags (or Goldeen)... both at level 10. Evolve into Poliwhirl at level 26 I believe... or use Super Rod to fish out level 23 Poliwhirls (in Red and Blue Super Rod's maximum levels are level 23) and use the Water Stone to get a Poliwrath... who still cannot learn anything >.<
[icon]071[/icon]: Use that Leaf Stone on Weepinbell... but try not to until you learn Razor Leaf at level 40ish (!!!!) ... but if you don't care for that just evolve it.
[icon]073[/icon]: Tentacool galore in the sea routes! They are all level 5-30... in multiples of 5. They evolve into Tentacruel at level 30... who is one of the few poisons that are usable in RBY.
[icon]078[/icon]: In Red and Blue find one Ponyta in Abandoned House and train until it is level 40 to evolve it. In Yellow they are at level 17ish instead of level 30ish and are found in the grass in Cycling Road. Good luck getting that thing to level 40 X_X
[icon]091[/icon]: Water Stone those Shellders you fish out with the Super Rod...
[icon]097[/icon]: Drowzees are found in the route to the right of Vermilion (Route 11 I think)... but evolving them takes until level 28 (or was it 33?) I forgot... but they are also catchable in the Unknown Dungeon in Red and Blue.
[icon]102[/icon] [icon]103[/icon]: Get an Exeggcute in the Safari Zone and evolve it with a Leaf Stone. Learns Stomp at level 28 and nothing more.
[icon]111[/icon] [icon]112[/icon]: Safari Zone for a level 25 Horn Attacking Rhyhorn that evolves at level 42... insane >.< Alternately wait until Unknown Dungeon for Rhydon.
[icon]113[/icon]: Tough to find and catch in Safari Zone. I found a level 9er once in Yellow. They are also in Unknown Dungeon so wait until there.
[icon]114[/icon]: Trade Venonat for one to the lady in Cinnabar Lab... or find one in the grass patch below Palette Town.
[icon]115[/icon]: Find one in Safari Zone. Sorry there are no other options >.<
[icon]118[/icon] [icon]119[/icon]: Good Rod for level 10 Goldeens. Super Rod for Seakings or evolve Goldeens...
[icon]120[/icon] [icon]121[/icon]: Fish out Staryus via Super Rod in Seafoam Islands and Water Stone Staryus to evolve them... but they do not learn anything >.<
[icon]123[/icon]: Safari Zone in Red and Yellow or Game Corner them
[icon]125[/icon]: Red only... at Power Plant... with just Quick Attack and Leer >.<
[icon]126[/icon]: Blue only... at Abandoned House... with just Ember >.<
[icon]127[/icon]: Safari Zone in Blue and Yellow or Game Corner them
[icon]128[/icon]: Tauros is only in Safari Zone... NOOOO!!!
[icon]130[/icon]: Evolve a Magikarp at level 20. Sorry, that is the ONLY way so far.
[icon]132[/icon]: Find them in Unknown Dungeon or in Route 15
[icon]134[/icon] [icon]135[/icon] [icon]136[/icon]: One Eevee per game, therefore only one choice... Water/Thunder/Fire Stone for respective eeveelution.
[icon]147[/icon] [icon]148[/icon] [icon]149[/icon]: Game Corner it or go to Safari Zone and fish out via Super Rod. In Yellow you can even find a level 15 Dragonair... who is TOUGH to catch! Dratini evolves at level 30 and Dragonair evolves at level 55... good luck training that thing.
Comparison
[icon]023[/icon] [icon]024[/icon] [icon]043[/icon] [icon]044[/icon] [icon]045[/icon] [icon]056[/icon] [icon]057[/icon] [icon]058[/icon] [icon]059[/icon] [icon]123[/icon] [icon]125[/icon]
[icon]027[/icon] [icon]028[/icon] [icon]037[/icon] [icon]038[/icon] [icon]052[/icon] [icon]053[/icon] [icon]069[/icon] [icon]070[/icon] [icon]071[/icon] [icon]126[/icon] [icon]127[/icon]
Red Versus Blue
[icon]023[/icon] [icon]024[/icon] < [icon]027[/icon] [icon]028[/icon]
Reasoning: Sandslash is more defensive and possibly one of the best Ground types in game. Arbok is just a giant snake with wacky stats and Poison typing... which is BAD
[icon]043[/icon] [icon]044[/icon] [icon]045[/icon] < [icon]069[/icon] [icon]070[/icon] [icon]071[/icon]
Reasoning: Defensive Poison types... are bad here. Victreebel actually has the speed (well, better than Vileplume), has the same special and higher attack. It can survive Moltres's Fire Blast in this game as well. But both get hit hard by Psychic anyways... I'd rather do something and get KOd rather than just get KOd. So I suppose Victreebel wins here... but both are all right I guess. But if you want a grasser, just use Venusaur or Exeggutor.
[icon]056[/icon] [icon]057[/icon] < [icon]052[/icon] [icon]053[/icon]
Reasoning: Due to the way the critical hit system worked, Persian was known for its critical hit hax. Persian is rather scary in RBY... and Primeape is a fighter automatically making it fail.
[icon]058[/icon] [icon]059[/icon] < [icon]037[/icon] [icon]038[/icon]
Reasoning: Ninetales has more original movepool like Confuse Ray and stuff... and has that amazing special of 100! Arcanine has the better stats but no movepool to speak of. Ninetales all the way.
[icon]123[/icon] = [icon]127[/icon]
Reasoning: Both are horrid... makes me wonder why they even have a typing. Scyther's Wing Attack only has 35 BP in RBY >.< Oh yeah, and Pinsir used to know Slash in this game... but afterwards, it was never able to learn it. I wonder why.
[icon]125[/icon] = [icon]126[/icon]
Reasoning: Neither are entirely useful... but if you trade back from GSC, Electabuzz can get some useful moves like Ice Punch and Magmar with Thunderpunch. Magmar is a lot stronger but has less speed. I would say they are dead even.