Animal Crossing started out on the Nintendo 64 as Animal Forest (Dōbutsu no Mori) before it was ported to the GameCube with additional content. Another version for GameCube, Animal Forest e+, included more enhancements, but was only released in Japan.

References

• Kapp'n, the "kappa turtle" that pilots the GBA Island boat, sings during every trip. One song refers to Mario. (Screen shot seen above.)
• When you start the game, Rover the cat will call Tom Nook on the phone. Sometimes when he calls, he starts the conversations with "Hey, it's-a me.... hahahah, good imitation, right?" This, of course, refers to the opening of Super Mario 64, where Mario greets you with: "Hello! It's-a me, Mario!"
• A red shirt emblazoned with the "M" logo from Mario's cap exists in the game as "big bro's shirt." Alfonso wears this shirt when he first appears in your town.
  
• Alfonso's catch phrase is "it's-a me."
• The "li'l bro's shirt" is like the "big bro's shirt," except it is green with Luigi's "L" logo. Louie (who, incidentally, looks sort of like Donkey Kong) wears this shirt when he first appears in your town.
  
• The "toad print" shirt resembles the design on Toad's hat... except the colors are reversed. Carrie wears this shirt when she first appears in your town.
  
• One rock per day drops a bag of bells when struck with your shovel. After the first hit, the rock turns red and begins to fade back to gray. During this short time, you'll get a bag of bells for each whack with your shovel. After three bags come out, the classic Mario 1-Up tune will play for each subsequent bag of bells you knock out. The tune is meant to clue you in to the fact that those bags contain a lot more bells...
• One time while talking to a villager, he acted scared and started the conversation with "Great galloping Goombas!" If you want to try to see it for yourself, here was the exact situation: A little after midnight, inside Aziz's house, choosing the second talk option ("Let's chat!", "Entertain me!", etc.). If you don't have Aziz in your town, anyone with the same "personality" as Aziz should say the phrase also (i.e. Genji and Teddy).
• When talking to Gulliver after getting a present, sometimes he'll refer to Toad Town (from Super Mario RPG and Paper Mario): "I wonder if my sweetie Mary in Toad Town has been doing OK since I left her... And I think of Helen often, since I left her heartbroken in Hyrule..." (Yep, a bonus Zelda reference too.) He then goes on to explain that the girls were his goldfish that he had to leave behind while traveling.
• If you have an e-Reader, scan Bob's e-card (Animal Crossing-e Series 1 #A-011 (sold separately)) and he'll send you a letter about his dream: "I was in the middle of one great catnap when I saw you in the strangest dream. You were running around on a tropical island with a water pump on your back!" This, of course, is referencing Super Mario Sunshine.

Cameo appearances

NES games
Several classic NES games in which Mario characters star, or make a cameo appearance, can be played in Animal Crossing (once you obtain the NES game items, of course).

• Donkey Kong
• Donkey Kong Jr.
• Donkey Kong Jr. Math
• Golf
• Mario Bros. *
• Pinball (cameo)
• Punch-Out!! (cameo)
• Super Mario Bros. **
• Tennis (cameo)
• Wario's Woods

* Mario Bros. is unlockable with a card from Animal Crossing-e Series 4.

** Super Mario Bros. is only accessible via the Action Replay cheating device for Nintendo GameCube. Before the game came out in the U.S., owners of the Japanese version were able to get a password to unlock SMB at a special Nintendo event in Japan.

Mario furniture series
Hidden in the game is special Mario-themed furniture, complete with wallpaper and carpet. The furniture was first discovered with universal passwords that were found by accident. Starting in January 2003, Nintendo released official passwords for each item in the Mario series in Nintendo Power (volumes 164 - 173).

• ? Block
• Brick Block
• Cannon (shoots Bullet Bills when activated)
• Coin
• Fire Flower
• Flagpole
• Green Pipe
• Koopa Shell
• Starman (when activated, plays the Starman theme and your character flashes)
• Super Mushroom
• Mushroom Mural (wallpaper)
• Block Flooring

Other Mario items available in the game (can be obtained during normal day-to-day playing):

• Mario trophy
• Luigi trophy
• Autumn medal (zoom in on it to see an outline of Mario jumping(?) inside the circle)
• Spring medal (see Autumn medal)
• big bro's shirt (see "References" section above)
• li'l bro's shirt (see "References" section above)
• toad print (see "References" section above)

Screen shots

• Coin, Autumn medal, big bro's shirt, Starman
• Close-up of Autumn medal
• Block flooring, ? Block, Mario trophy, Luigi trophy, Super Mushroom