If you you use an Action Replay, you can access the paper airplane item in your inventory. If you place the item on the ground, walk off screen, and come back, the paper airplane will duplicate itself. Pressing the A button while on top of the paper airplane will make it disappear visibly, but will still exist in the system's memory. Letting the airplane multiply too much can crash the game.

The NES games Balloon Fight, Baseball, Clu Clu Land, Clu Clu Land D, Donkey Kong, Donkey Kong 3, Donkey Kong Junior, Donkey Kong Jr. Math, Excitebike, Golf, Ice Climber, The Legend of Zelda, Mario Bros., Pinball, Punch-Out!!, Soccer, Super Mario Bros., Tennis, and Wario's Woods can be played in the game. They can be acquired through Game Boy Advance connectivity, e-Reader, and secret codes to Tom Nook. However some can only be obtained with the use of a cheat device which can also unlock all of them at once.

Animal Crossing is only one of five different versions of the same game, three of which were only released in Japan, and one of which was only released in China. The first version was for the Nintendo 64 in 2001, entitled "Dobutsu no Mori", which translates to "Animal Forest". The second version, "Dobutsu no Mori+", was an enhanced remake of the original game, released on the GameCube. This was the version that would be localized as Animal Crossing in North America and Europe. The fourth version, "Dobutsu no Mori e+", was a second enhanced remake released on the GameCube including e-Reader card content. The final version was a Chinese localization of the original Nintendo 64 version, Dòngwù Sēnlín, released five years later in 2006 exclusively for the iQue Player.

Within the game's data is an unused squirrel character, named "Shakitto" (シャキッと, meaning "crisp" or "crunchy") in the Japanese version's files. The text "Rya~" (りゃ〜) is also placed directly after her name, though it's unclear whether this is meant to be an additional component of it or if it was a catchphrase.

Despite Shakitto appearing to be a scrapped villager, her filename, ac_ev_dokutu, indicates that she was likely conceived as a special character. The "ev" component is used in the game's data for special characters that occasionally visit the player's town rather than being permanent components (e.g. Redd, Sahara, Wendell, Gracie, etc.), while "dokutu" is likely a truncation of "dokutsu," which can refer to either a cavern or a hole in the ground. The latter implies that she would've buried items for the player to dig up, similarly to an action that villagers can announce on the Bulletin Board in the final game.

Because no other code for Shakitto's intended function remains in the final game, spawning her in as a villager with Action Replay codes instead results in her using various bits of preexisting character data.

The train conductor 'Porter' is based off of the Japanese song 'The Monkey Palanquin Carrier'. This is the reason he's a monkey.

The "forest map select" from Doubutsu no Mori still exists in the game's code, but there's no easy way to access it.

The game has an entire debug mode which can be activated by setting the disc ID version field to 0x99 through using a hex editor and change byte #7 (0x00000007) of the ISO/GCM file. It works on all versions of the game.

There are numerous unused items in the game's code, all of which can be accessed with cheats. These include:
• A blue fish, possibly used to test the fishing function.
• DUMMY, a glitch item appearing as a white triangle with Japanese text on it reading "ダミー", which translates to "DUMMY", hence the name. Once in an Igloo, you obtain the item in a similar way to other furniture. The animal might want to play a game where he or she will ask you to pick two cards. One card you have to buy something and one card you will get a free prize. The prize card may sometimes be a DUMMY card.
• MBG, a glowing yellow box that moves back and forth, can push the player around (sometimes making them float), and can modify the spread of Paper Airplanes.
• A tool labeled "Sickle", which makes the player function as if they had nothing in their hands. This item dates back to the development of the original Doubutsu no Mori, with an early inventory sprite for it appearing among assets uncovered in the 2020 Gigaleak, a large-scale breach of internal server data from Nintendo. The item appears as a toolbox when dropped, a feature present in Doubutsu no Mori (as well as several later games in the series) but not in Animal Crossing.
• An "Unknown Item" that appears in the player's inventory as a box with a question mark, and appears in homes as a clone of the DUMMY item.
• Paper Airplanes, which, if you place on the ground, walk off screen, and come back, will duplicate itself. Letting the airplane multiply too much can crash the game. Pressing the A button while on top of a paper airplane picks it up, and the player can then throw it using the Z button; however, they cannot move after it lands, softlocking the game.

If the player goes to another town and resets the game before going back to their town, the next time they load up their profile they will start with a Gyroid face.

The international release of Animal Crossing overhauls the designs of two different characters due to their Japanese designs being evocative of black and Asian racial stereotypes. In Doubutsu no Mori and Doubutsu no Mori + (the Japanese version of Animal Crossing), Jane is shown to have dark brown skin, white fur, tired eyes, and large, pink lips, making her resemble a blackface caricature. Meanwhile, Chip's original design gives him squinting, slanted eyes and large glasses, which in combination with his buck teeth makes him unintentionally resemble stereotyped caricatures of Japanese soldiers in American propaganda during World War II. In Doubutsu no Mori e+, Jane and Chip revert to their original designs. Despite this, the photo in Chip's booth still depicts his international design, which would become standard in all later installments.

Mr. Resetti was added into the game when developers noticed that, during play testing of Animal Crossing, many players were resetting their consoles to let the stock in Tom Nook's store change. They felt that this was toying too much with the game's mechanics and added Mr. Resetti in to discourage this behavior.

A mole named Mr. Resetti will pop up to scold the player if they reset the game without saving. On the sixth and random subsequent times, he will force the player to copy what he says by typing it in, and will not leave until they do so correctly. However, typing in the following phrases will trigger special dialogue where Mr. Resetti scolds the player even more:

"no", "NO!", "jerk", "Die!", "Loser", "RESET", "freak", "Creep", "no way", "Leave!" "No Way!", "shut up", "go away", "Pinhead", "Dirtbag", "Scumbag", "Shut Up!", Go Away!", "Butthead", "Bite me!", "U R UGLY", "groundhog", "You stink", "I + Reset", "You suck!", "I hate you", "Moles suck", "Who Cares?".

Sometimes villagers will request the player to track down their "Pokémon Pikachu". This refers to the virtual pet toy of the same name, rather than the creature itself.

Animal Crossing for the GameCube is a direct port of the Japanese-only Nintendo 64 Doubutsu no Mori (Animal Forest) so it takes up very little space on the GameCube disc. The entire game is loaded into the GameCube's RAM, and as a result, after the player enters their town they can remove the game disc from the GameCube and continue to play the game normally.

When the player meets Mr. Resetti for the sixth time, one of his lines reads "You got another think comin'!!!" This line contains a typo by mistakenly saying "think" rather than "thing."

On August 7, 2002, Nintendo held a contest called the Animal Crossing Official Pioneers Program, where a limited number of participants would be able to receive an early-access copy of Animal Crossing. To apply for selection, one would have to submit a short response of 50 words at most explaining why Nintendo should pick them to be "Animal Crossing Pioneers", with 125 teams of two people (totaling to 250 applicants) ultimately being chosen. Each winner was provided with a specially-marked promotional disc for Animal Crossing, a 59-block memory card, and a calendar spanning September 2002 to December 2003; in addition, winners were given access to an online forum where they could interact with Nintendo of America staff members, completing in-game objectives, providing feedback, and participating in online chats.

In an early announcement trailer for the Nintendo GameCube, Animal Crossing was called (or at least promoted as) "Animal Forest for Nintendo Gamecube", outright referencing the original Japanese title of the game (Dōbutsu no Mori or "Animal Forest" in English). This suggests that either the English localizers were thinking of keeping the game's original title, albeit translated, or the title "Animal Crossing" was not yet finalized.

When waking a villager with the "normal" personality type up from a nap, one of the phrases they can say is "This is not my beautiful house, [catchphrase]! How did I get here?" This is a reference to two different lyrics from the Talking Heads song "Once in a Lifetime" released in 1980.

In the Japanese version, Dōbutsu no Mori +, two paintings that were present in the original Dōbutsu no Mori, the Dreadful Painting and the Novel Painting, are not obtainable in the normal course of play. However, they still exist in the game's code and can be legitimately brought over to a player's save file by importing one from Dōbutsu no Mori (via Nintendo of Japan's now-defunct Data Moving Service), though they can't be donated to the Museum. In the international release of Animal Crossing, however, these paintings are completely removed, and their index numbers instead point to duplicates of the DUMMY furniture item.

It's likely that the decreasing accessibility of these paintings was due to the fact that their real-world equivalents, Edvard Munch's "The Scream" and Piet Mondrian's "Composition with Red, Yellow, and Blue", were still under copyright at the time. The Munch and Mondrian portfolios wouldn't enter the public domain until 2015, well after the Dreadful and Novel paintings were retired from the series.

Several clothing items were changed between the Japanese and international releases of the game:

• The Three Arc Shirt (a.k.a. the Familiar Shirt) is replaced with the Fortune Shirt, due to the former's resemblance to Charlie Brown's shirt in the American comic strip Peanuts (which had ended its print run in 2000, shortly before the game's release).
• The Tomato Juice Shirt is replaced with the Fishbone Shirt, due to the former's design resembling bloodstains.
• The W Shirt is replaced with the Houndstooth Tee, due to the former's resemblance to the logo of American fast food chain McDonald's.
• The Puzzling Shirt is redesigned to use more pastel colors, also changing the bottom-center square from orange to purple, to reduce the design's similarity to the Rubik's Cube brand of toy puzzles.
• The I Love GC Shirt (itself a redesign of the I Love 64 shirt from Dōbutsu no Mori) is replaced with the Cherry Shirt, due to the former being a parody of the I ❤ NY logo, which is trademarked by the New York Department of Economic Development.

These redesigns are also carried over to Doubutsu no Mori e+.