From Bulbapedia, the community-driven Pokémon encyclopedia.
Cheating is a highly controversial but frequently used method of playing the Pokémon games. It is notably used to duplicate rare and valuable items and to obtain certain legendary Pokémon which would not be available until a Nintendo event otherwise.
Methods of cheating
Perhaps one of the greatest source of rumors in the Pokémon fandom is fake glitch methods. These are often described to sound more like easter eggs than glitches.
The most notorious example of this is rumored methods of finding Mew which were very common during the Generation I era. These have become an inside joke of the fandom, and some fans will invent absurd methods to make Mew appear in the game.
However, there is a way to get Mew in all the Generation I game versions known as the Mew glitch.
Some cheaters will use devices like an Action Replay to affect the execution of the game and easily obtain things they would otherwise need to work for. This is one of the most controversial methods of cheating because it is deliberately altering the gameplay experience, rather than exploiting something already in the game.
Cheating devices are commonly used to get Pokémon or items which are otherwise only obtainable through a Nintendo promotional event, if at all. Commonly, in Generation II and III, this means using the device to gain a special item to catch a Pokémon, such as the GS Ball or Old Sea Map. In Pokémon XD: Gale of Darkness, Bonsly is completely unobtainable without the use of a cheating device. In Pokémon Diamond and Pearl, a code which has been come to be known as the "walk anywhere code" allows cheaters access to any remote location by simply walking from one map location to another, sometimes passing through the Mystery Zone. This code also enables users to catch the Pokémon Shaymin and Darkrai. The "Wild Pokémon Modifier" code is perhaps the most useful cheat, used to make any Pokémon of choice appear in any location (an updated version of the modifier allows the player to set level and nature), readily available for capture to build a collection of an unlimited amount of desired Pokémon easily with no negative effects to the save file. The Modifier also makes EV-training much easier.
With cheating devices, cheaters can also simply alter the game's code to give them many other valuable Pokémon, making the hunt for Shiny Pokémon and those with optimal IVs and natures incredibly easy. This method of gameplay can irritate other players, particularly when they receive blatantly hacked Pokémon at the GTS.
Using the downloadable program, Pokésav, in conjunction with an Action Replay DS or a Rom Cart like the R4, allows one to literally make their own Pokémon from scratch.
However, not all players will use cheating devices to make the game easier. In some cases, cheating devices are actually used to make the game harder, such as the case where a player would use a code to trigger a battle with Professor Oak.
The primary complaint against cheating methods is that it takes no particular ability to exploit a glitch or enter a cheat code, and thus detracts from the point and spirit of the game, making it less enjoyable. While this is a subjective matter, it is the primary cause of cheating offending most players.
Another more practical argument against cheating is that glitches and cheat codes often hurt the stability of the game. Many players have lost their Pokémon or save files while trying to exploit their game. Occasionally entire parties of Pokémon will be overwritten because of a destabilized glitch.
Some will justify using cheating devices to get Pokémon when they cannot attend Nintendo promotional events, the only legitimate way to get these Pokémon. Whether or not this is a valid excuse for cheating is a matter of opinion.
To combat cheating, all games from FireRed and LeafGreen onwards have two measures to prevent cheating. Firstly, Mew and Deoxys were given special programming that prevents them from obeying the player if they were obtained illegitimately. However, this countermeasure fails if the player uses cheats to get to Faraway Island or Birth Island, and then catches the Pokémon in a somewhat legitimate manner. Secondly, special programming called DMA (Dynamic Memory Allocation) is used in the games, and causes the data targeted by cheating devices to dynamically move around. However, cheaters got around this simply by using codes to disable the DMA. The Generation IV games do not use the DMA, though.