Action Replay Codes
The Action Replay cheating device for the Nintendo DS lets you edit certain aspects of your games through codes. Action Replays come with lists of codes already on them for most popular games. To use the device with a game, you insert the Action Replay into your Nintendo DS, then insert your game into the Action Replay. While you sometimes have to enter the codes manually, the device's interface lets you quickly enter new codes for your games that you find online.
Wild Pokemon Modifiers
"Pokemon Black Version," "Pokemon White Version" and many previous Pokemon games have Action Replay codes to specify which wild Pokemon you'll encounter next. Some games use individual codes for each Pokemon. For example, if you wanted to catch Charmander, you would enable the Charmander-specific code. After enabling the code, the next wild Pokemon you encounter is Charmander. Other games approach wild Pokemon modifier codes differently. The code deposits a certain number of Master Balls into your bag, corresponding with the total number of Pokemon in that game's National Pokedex. You then throw away Master Balls until the number you have left corresponds with the Pokemon you want to catch. Since Charmander is the fourth Pokemon in the National Pokedex, you'd toss all but four Master Balls to encounter Charmander in your next wild battle.
Shiny Codes
In the video games, every Pokemon has a shiny version. These rare versions feature a different color pallet, making the Pokemon look different. While they don't offer any stat bonuses, the rarity of shiny Pokemon without codes makes them collectible. Using the proper Action Replay code, you can force the game to make every wild Pokemon you encounter shiny.
Level Modifier Codes
Pokemon level modifier codes alter the level of wild Pokemon you encounter. Pokemon regularly appear within a specific set of levels depending on where you encounter them in the game. Pokemon near the beginning of the game are lower leveled, making them easier to catch, but weaker than high-level Pokemon. The level modifier codes let you set the level beforehand, so you can always encounter Pokemon at a certain level between one and 100. Since higher-level Pokemon present more challenges while catching them, these codes are best used with a code that makes Pokemon easier to catch, or a code that gives you Master Balls. Master Balls let you catch any Pokemon you throw them at, ensuring they never escape your capture attempt.
Considerations
When entering your codes, pay attention for any special instructions. For instance, the wild Pokemon modifier codes for "Pokemon White Version" and "Pokemon Black Version" require you to press "Select" on your Nintendo DS to activate the code once your game starts. When you're done using your code, save your game and reset your Nintendo DS, then disable the code within the Action Replay menu.