The article "the" is used when announcing trainers for battle (for example, Charlie the Bug Catcher. It worked for typical trainers but not Gym Leaders, Elite Four, your rival, or link battles. A screenshot in the instruction manual of the English Red and Blue still contains the text "The Brock wants to fight!", possibly suggesting a late removal. The instruction manual also calls them Pokemon Leaders, instead of Gym Leaders.

Kingler's front-facing sprite erroneously depicts its claws as equal in size, when in reality the right claw is actually much smaller than the left.
Strangely enough, in the original Japanese Red and Green versions, the claws are their correct sizes. The claws are once again their correct sizes in Yellow version.
Additionally, the side that the larger claw appears on was changed after Generation I. The bigger claw became the left claw while the smaller claw became the right.

There's a mistake on Cloyster's sprite. It shows its shell positioned horizontally instead of vertically.

The blurb on the back of the boxes states that 139 different Pokémon can be obtained in each game without trading. This, however, includes all Pokémon that the player must choose between (i.e., both the Omanyte and Kabuto families are counted). Therefore, the true total of different Pokémon obtainable in one adventure without trading is 124, which excludes the two unchosen starter families, one Fossil family, two Eeveelutions, one of Hitmonlee and Hitmonchan, and the four Pokémon that only evolve when traded.

The old man, who is laid down protesting his lack of a morning coffee in the localized version, is actually passed out from drunkenness in the Japanese version. You would have to bring him coffee in order to sober him up.

Red and Blue's default names in the game's coding are Ninten and Sony, respectively, a reference to Nintendo's rivalry with Sony in the gaming industry, i.e. the Playstation vs. the N64.

There is a glitch where the player can fish in large statues found in gyms and Indigo Plateau, even being able to catch Pokemon. You can find Magikarps with the Old Rod, Poliwags and Goldeens with the Good Rod, and Krabbies, Psyducks, and Goldeens with the Super Rod. The Super Rod only works in the Cerulean City gym. You can also surf on these large statues, but no Pokemon will appear while surfing.

There were originally going to be 190 Pokemon instead of 151; 39 of them were later moved to Pokemon Gold and Silver. By checking the game's code, you can see the orders in which the Pokemon were entered into the game, Rhydon being first and ending with Victreebel. Since Ken Sugimori, the designer of the Pokemon, confirmed that Rhydon was the first Pokemon ever designed, it can also be inferred that the Pokemon were put into the game in the order in which they were originally intended to appear in the Pokedex. The ordering also proves that all 190 Pokemon were conceived before the original games' release.

Charizard was unable to learn Fly in Red & Blue. This was changed in Yellow which also made it possible to get a Charizard with Fly in Red & Blue via trading.

The original Red and Green Versions were supposed to have a female trainer along with the male trainers, Red and Blue. She was most likely removed due to hardware restrictions, but is still seen on the official strategy guide and artwork. The character was used as the character 'Green' in the comic and 'Leaf' in the remake, FireRed and LeafGreen.

Dratini's sprite as found in Red, Blue, and Green (both the original Japanese release and the updated International release with different sprites) Versions has stripes on its belly. These stripes were removed in Yellow Version and have not reappeared since.

Mew was the first Pokemon name to be trademarked, even before the name "Pocket Monsters".
Mew was trademarked 1990, while Pocket Monsters was trademarked in 1995.

Mew was secretly added at the very end of development and was initially not intended to appear in the game. However, due to a glitch, Mew started to appear seemingly naturally (i.e. without GameShark and the like) in some peoples' games.

The three legendary birds (Articuno, Zapdos, and Moltres) are puns on elements, as well as numbers in the Spanish language. Articuno is Arctic (ice) and uno (one), Zapdos is Zap (electricity) and dos (two), and Moltres is Molten (fire) and tres (three). This is also the order that they appear in the National Pokédex.

In Copycat's bedroom is a SNES with a game featuring Mario with a bucket on his head. This is a reference to the Japan-exclusive game Mario & Wario, another Nintendo game developed by Game Freak.

During the Professor Oak lecture at the beginning of the game, a Nidorino will be shown as an example of a Pokemon. However, the cry that plays belongs to a Nidorina.

When you encounter your rival in Pokemon Tower, he will ask you why you're in the tower to begin with because you don't have any dead Pokemon to mourn over. This implies that he has lost a Pokemon and has come to pay homage to it or lay it to rest. Furthermore, his Raticate from the previous battle on the S.S. Anne is replaced by an Exeggcute, Growlithe, or Gyrados, depending on the starter Pokemon you chose. This seems to imply that his Raticate somehow died between the battles against him on the S.S. Anne and in Pokemon Tower; common fan speculation states that the Raticate died from wounds received from the battle on the S.S. Anne.

The game contains the now infamous line: "Hi! I like shorts! They're comfy and easy to wear!" The line became a meme among the Pokemon community, and was referenced in Pokemon Black 2 and White 2.

Ninetails was inspired by a powerful, fire-breathing fox with nine tails from Japanese mythology.

During development, a type called "Bird" was going to be in the game, but was later changed to flying. This is still in the game's code, with Missingno. being a bird/normal type.

Pokemon Red & Blue were originally supposed to allow players to use badges as an item. When used outside of battle, a looped version of one of the jingles played after Oak evaluates the player's pokedex progress will play. Only the Boulder Badge and Cascade Badge were usable in battle and were able to throw a rock or bait at a Pokemon, like in the Safari Zone.

Concept art shows a shop owner with a Pokemon on a shelf. This may indicate that Pokemon were originally going to be sold in shops.

In Pokémon Red, Blue, and Yellow, as well as their remakes Fire Red and Leaf Green, a truck was placed in the S.S. Anne's port. The truck seems to serve no purpose. Its presence in the remakes could be a reference to the original rumors that Mew could be found under the truck.

In the Pewter Museum of Science in Pewter City there is an attraction featuring a space shuttle. In Red & Blue, the plaque accompanying the space shuttle model reads "Space Shuttle Columbia"; however, in the Generation III remakes the plaque simply reads "Space Shuttle". This is probably due to the fact that on February 1, 2003, the real Space Shuttle Columbia disintegrated upon re-entry during its 28th mission, killing all seven crew members. The reference to Space Shuttle Columbia was kept in the Japanese version of the Generation III games.

There is an exploit that, when used correctly, allows your Ditto to trick a wild Pokemon into using Transform.

This is only possible with the Pokemon Pidgey, Pidgeotto, Spearow, or Fearow as they are the only wild Pokemon who know Mirror Move. If your Ditto uses Transform on a wild Pokemon who uses Mirror Move in the same turn, The wild Pokemon transforms into Ditto. The game also registers the wild Pokemon as Ditto.

In the Kanto region, all of the towns are named after colors, the only exception being Pallet Town, which was named after the word "palette," or a range of colors used by an artist or in a picture.

There is a man who is located at Cinnabar Island's Pokemon Laboratory who requests a Raichu in order to trade for an Electrode. After the trade is complete, the man then says 'The RAICHU you traded to me went and evolved!'

This is a translation error where the Japanese version of Pokemon Blue has a Machoke in place of Raichu where as Pokemon Red and Green have Raichu.

In the game's code there is a trainer class for "Chief" called シルフのチーフ (Shirufu no Chīfu) which translates to Silph's Chief. This possibly meant that the player had to battle Silph Co.'s president.

The Pokémon sprites were changed in Japan for their special edition of the game, Pokémon Blue. Originally, Pokémon Red and Green had different sprites to those of the English release. These new sprites were used in the international release of the game. It's widely agreed that the revised version in Pokémon Red & Blue are far superior to those in Pokémon Green, where a lot of proportions were out of place.

There is an unused item written in the code of the first Pokemon games that would allow the player to ride on water without having a Pokemon use Surf. It has been given the fan name "Surfboard"

The Japanese names of Vaporeon, Jolteon, and Flareon are literally Showers, Thunders, and Booster.

Koffing's sprite is wrong. The artist drew the skull and bones above its face rather than below.

The hotel in Celedon City has an invisible PC in the corner. If you stand one space down from the top right corner of the first room and press A, you'll be able to boot it up. It's assumed that this is a slight oversight, as the hotel resembles a Pokemon center, and the programmers removed the PC graphic but not its function.

There is evidence to suggest that Ditto is a failed clone of Mew. Both Pokemon are genderless, weigh the same, their base stats are exactly the same in every respect, they share almost identical colors, and they're the only two Pokemon who learn Transform naturally.

Ditto can also be found commonly in the same cave as Mewtwo, as well as the mansion on Cinnabar Island, where experiments on Mew were said to take place.

The game was originally planned to feature 190 Pokemon. 39 of them were cut out and later used in Pokemon Gold & Silver.

There's a battle against Professor Oak programmed into the game, but was never included in the final game. It is only accessible by using a Gameshark or glitching the game.

His team consists of: lv.66 Tauros, lv.67 Exeggutor, lv.68 Arcanine, lv.70 Gyarados and the starter Pokémon that neither you or your rival chose at the beginning of the game, fully evolved at lv.69.

According to a journal entry in the game, Mewtwo's birthday is February 6th.