There are only 37 unique sounds for all 151 Pokémon cries. Effects such as modifying the speed and pitch are applied to those 37 base sounds to make the different cries for each Pokémon.

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.

The Route 24/25 theme has a strong resemblance to the Sky Theme from Mario & Wario, a Japanese-only Super Nintendo game which was also developed by Game Freak.

The infamous Missingno glitch can be triggered by the player having Pokemon knowing the moves "Fly" and "Surf", going to Viridian City and triggering the Old Man's catching tutorial. Afterwards the player must Fly immediately to Cinnabar Island and surf along its eastern coastline without moving away from it or back onto the island itself, eventually triggering an encounter with Missingno (Or a similar glitch Pokemon named 'M), after which the item in the player's 6th Item slot will be duplicated to a maximum of 255.

This glitch is triggered by the game's internal data replacing the player's chosen name with the "Old Man" string for the sake of the tutorial and it not being properly replaced by another battle. Whatever letters are used in the player's name will also change what form Missingno will take. For example, a W being used as the 3rd, 5th or 7th letter will trigger the Kabutops Skeleton Form Missingno, an X will trigger the Aerodactyl Skeleton Form and a Y will trigger its Lavender Tower Ghost Form.

It's possible to initiate a glitch that allows the player to walk through walls by use of the Safari Zone's limited steps, and having a poisoned Pokémon. By having the game think that you're still within the Safari zone while outside, and jumping over a ledge on the 500th step, the game will send the player back to the entrance of the Safari Zone while still having it within its data that they are currently mid-jump. When exiting a building with this glitch active, the game will crash, but it's possible to exit the entrance room of the Safari Zone by having the player's Pokémon die of poison. Using this glitch allows the player to skip certain sections of the game, but is riddled with a number of limitations.

Promotional material for the game lists Paras with the name "Parasyte". This name may have been changed in order to avoid copyright issues with the 1990 manga series, Parasyte.

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.

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.

In an interview with Yomiuri Online, Pokemon designer Atsuko Nishida revealed that the reason why Pikachu was made a rare encounter in Viridian Forest was because of her own personal favoritism towards the character and what she described as a feeling of "not wanting to let other people have Pikachu."

In 2020, an unreleased extended cut of the 1998 Pokémon Generation I bus commercial was uploaded to YouTube. This extended cut shows that the bus featured in the advert was actually crushed during production, despite the final commercial cutting from the compactor starting to the compactor having already crushed the bus. The unreleased crushing scenes do not have Pokémon superimposed into the windows.

In the original Game Boy release of Pokémon Red and Blue, examining the television in the living room of the player's home in Pallet Town from the side would show the message: "Oops, wrong side..." In the Generation III remakes, Pokémon FireRed and LeafGreen, the aforementioned TV has been positioned against the wall in such a manner that it cannot be approached except from the front, facing the TV screen. However, by using a cheat device to enable a player to walk through walls, then approaching the TV from the side through this method, it will show the same message, despite being impossible under normal conditions.

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.

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.

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 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.

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

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

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 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.

In the game's code there is a trainer class for "Chief" called "シルフのチーフ" which translates to Silph's Chief. This possibly meant that the player had to battle Silph Co.'s president.