According to NeoSeeker, the GameShark code to get wild Pokemon to spawn at level 100 in “Pokemon LeafGreen” is 56307399 25DF4466. For this code to work, the player has to first enter the master code CCD017E8 EF04228C.
When using the master code, players can choose any level at which wild Pokemon spawn. For example, to make the game easier, players can choose to have wild Pokemon spawn at level one by entering in code 8BB602F7 8CEB681A. Other level-controlling codes listed on Neoseeker are radically different. Although there is no code for players to change the gender of the Pokemon they have already caught, they can choose the gender of the Pokemon spawned in the wild. To make all wild Pokemon female, the code is EB34F751 A96B854D 78DA95DF 44018CB4. To make all wild Pokemon male, EB34F751 A96B854D 141BB87C 83D7018F should be used.
Players can manipulate their games in other ways by using GameShark codes. For example, when visiting the day care, players can make it free by entering 6F1FF3B5C2EF. They can also turn on quick leveling by entering the code E6343C0CCC28 6F5DCD154C62. Players who are trying to breed Pokemon at the day care can turn on quick egg hatching by entering 908D349E3D92.