There are many ways for players to gain EXP fast in Pokemon Brilliant Diamond and Shining Pearl aside from battling wild Pokemon and Trainers. These methods involve on several holdable and Key Items, as well as partnering several NPCs.
Eevee is one of the versitile Pokemon players can have in Pokemon Brilliant Diamond and Shining Pearl thanks to its Eeveelution, or the ability to evolve into different forms. But in order to have the said Pokemon, they need to catch it, as well as meeting several conditions in order to evolve it.
Players of Pokemon Brilliant Diamond and Shining Pearl will have the opportunity of catching Legendary Pokemon in the game by unlocking a special area called the Ramanas Park.