A recurring oddity in the Pokémon games is that the Gym Leader and later Elite Four member Koga, the Kanto Region's Poison-type expert, threatens to defeat his opponents with both Poison and Sleep tactics. In Red and Blue, he states:


In Gold, Silver, Crystal, and their remakes HeartGold and SoulSilver, he states:


In FireRed and LeafGreen, he states:


Despite this, the only game in the series where Koga's main team uses any Sleep-inducing moves is Yellow, where two of his Venonats have Sleep Powder. In contrast, all of Koga's teams have incorporated Poisoning moves, with some of his teams being entirely composed of Pokémon using such moves. Although possibly a mistake, this might also tie into the theme of misdirection, which would be fitting for the ninja-themed Fuchsia Gym.

When the game was initially released in Japan, it was only available to people who bought a copy of the November 1996 cover-date issue of Japanese magazine CoroCoro Comic and filled out a mail-order form for the game. This promotion lasted from the day the issue was released on October 15 until December 27, 1996. As a result, on some official Japanese Nintendo and Pokémon websites, October 15, 1996 is listed as Pokémon Blue Version's first release date in Japan before it received a wider retail release there on October 10, 1999.

In a 1997 interview with Famimaga 64, Satoshi Tajiri said that the Pokémon Porygon was made due to people saying that he should develop a 3D game instead of a sprite-based game on the Game Boy:

In an interview with Junichi Masuda, he stated that the source data for the game was almost lost because the computer that stored the data suffered from a nasty crash.

In the Pokemon Origins anime miniseries, Red uses a Charizard, Dodrio, Persian, Scyther, Lapras and Jolteon during his fight against Blue at the Indigo Pleateau. These were the same Pokemon on the team used by creator Satoshi Tajiri during his test playthrough of Pokemon Red & Blue.

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.

The 7th gym leader originally had a different design. Because of its similarities to early artwork to Blaine, as well as his appearance in the anime, this design is likely the original design for Blaine.

Ken Sugimori revealed on his Twitter that Brock was originally meant to be the second Gym Leader, with what looks like a Youngster being the original first Gym Leader.

On Cinnabar Island if you don't have the key to the gym with you there is a small glitch you can perform. First, use Surf on the right hand side of the island and move upwards until you're across from the door. Get off your Pokemon and walk until you're in front of the gym door where you'll get the message about it being locked. Look up and you'll see an old man on the roof while this text is displayed.

Indigo Plateau's background music sounds very similar to the Mother 1 (EarthBound Beginnings) Mt. Itoi theme.

The international versions of Red & Blue are based on the Japanese version of Blue. Many changes were made in this version, including updated graphics and sound, as well as several bugfixes found in the Japanese versions of Red & Green.

After Shigeru Miyamoto became Satoshi Tajiri's mentor, Satoshi gave thanks to him by making the default rival name 'Shigeru'. Satoshi made himself the default name for the protagonist. This can be found in the Japanese Generation I Pokemon games.

Some Pokemon share the same cries. Some examples are Charizard and Rhyhorn, Ditto and Poliwag, and Goldeen and Caterpie.

Drowzee's sprite has five fingers. It is supposed to have three.

The Spanish translation of the first generation Pokémon games is known for being very poor quality with many translation errors. One of the most remarkable mistakes is the translation of the move "Slam" into "Portazo", which actually means "Door Slam". This name remains even in the latest games (5th Generation).

In the Pokemon Red and Blue beta, Cubone was originally known as "Orphon," a corruption of the word "orphan," based on its abandonment at birth.

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.