Box trick
The Box trick is a method in the Generation I and II Pokémon games that allows a Pokémon to gain effort points without necessarily leveling up in the process. This method is most useful when training a Pokémon that is already at level 100.
Usually, a Pokémon gains stat points when they level up, based on the amount of effort points that the Pokémon has acquired through battle, and based on its own base stats. But by depositing a Pokémon into the PC and withdrawing it, the game will, in the process of depositing/withdrawing, recalculate the stats of the deposited Pokémon based on the amount of effort points etc. it possesses. The reason it does this is because while in the box the actual stat values are not stored, so they must be calculated when taken out or viewed.
A Level 100 Pokémon in Generation III and IV is unable to gain effort points though battle, so this trick cannot be used to increase a Level 100 Pokémon's stats in those games. This is because Effort Points are awarded at the same time as Experience Points, and since Pokémon at Level 100 don't gain Experience, they are also skipped over for Effort Points. A Pokémon at Level 100 can still gain Effort Points by consuming Vitamins. That said, a Pokémon can still see the extra stat points earned from Effort Points without leveling up with this trick even if they are not Level 100.
