An Action Replay is a cheating device that is used to hack into the Nintendo DS or Nintendo DSi's system to cheat. In the case of Animal Crossing: Wild World, it can make every item available and cause the player to have maximum Bells. This results in the game beginning to glitch. Action Replays also can create items (such as seeds) and can seriously damage the DS systems if used in a certain way. It is also often used for the Villager Modifier.
Also, the Action Replay does not work on DSi's due to Nintendo increasing the security on it. The creators of the Action Replay later released the Action Replay DSi allowing people to cheat using a DSi. In Animal Crossing for the GameCube, it is possible to obtain Mario Bros., Ice Climber, Super Mario Bros., and The Legend of Zelda, but Mario Bros. and Ice Climber are also obtainable through e-reader cards.
Animal Crossing (GCN)
Using an Action Replay on Animal Crossing GameCube, it is possible to give yourself certain items (such as the snowman set) or modify the bug/fish log to say you have caught everything available. You can change your player's gender, you can also grow and shrink, using the C control stick, and you can jump using the Z button, which can be used to get onto the train track, jump into the river and get to the island. By doing so, it may be possible to catch the whale, although video footage shows that doing so will freeze the game. You can also plant instant trees which disappear after you exit the game. You can hack into villager's profiles, and more.
Animal Crossing Wild World
Wild World is capable of many Action Replay codes. Built into the Action Replay are codes that give you an infinite supply of any item (not including 'not used' items by default), infinite bells, reduce your mortgage by huge amounts, remove weeds and so on. There are also programs, such as AnimalMap, which can create powerful codes to change acres in your town, spawn items on the world map, duplicate buildings and give you 'seeds' - buildings that are held in your inventory, which make buildings when dropped. Jumping is not possible, as Wild World has no Z axis for players and animals.
Animal Crossing City Folk
City Folk has next to no Action Replay codes, but uses game saves instead. Game saves can be installed using Action Replay for Wii, but more people use the Homebrew Channel.
Ocarina codes, the alternative for Action Replay codes on the Wii, can be used instead by using a USB loader, which can be installed on the Homebrew Channel. A lot more Ocarina codes are available for City Folk, compared to Action Replay codes. It is, however, not recommended as the use of a USB loader is often considered illegal.