Much like the similarly-named Choice Scarf and Choice Band, the Choice Specs buff one of its wearer’s stats while restricting the user’s offensive options to one move. In the case of the Specs, it’s the wearer’s Special Attack is boosted, meaning that most elemental moves (Flamethrower, Hydro Cannon, Thunderbolt, etc.) will receive buffs thanks to this item. Here’s where you can find the Choice Specs in Pokémon Brilliant Diamond and Shining Pearl.
Like the other “Choice” items, you can purchase the Choice Specs for 25 BP at the Exchange Service Corner (BP Shop) in the Battle Park — an area only accessible following your conquering of the Elite Four and unlocking of the National Pokédex. You can fight opponents in the Battle Tower to earn BP, which can be used at the BP Shop.
However, unlike the other “Choice” items, you can find this one elsewhere on the map, but only during a certain time. Head to Celestic Town before 10 AM and go to the building in the northwest corner of the town. Talk to a sunglasses-wearing man inside the building and he’ll tell you about how glasses can — quite literally — change the way you view the world before handing you the Choice Specs.
Once you give the Specs to a Pokémon, its Special Attack stat will be buffed by 50%. When used in conjunction with the game’s more powerful elemental moves, such as Blast Burn or Draco Meteor, it can make your Pokémon a truly catastrophic offensive force to be reckoned with. That said, remember that it only allows your Pokémon to use one of its four moves; it’d be a shame if an Electric-type got a buff only to be confronted with a Ground-type.