Like the Mystery Gift in the main games, the Pokédex 3D Pro accepts gift codes that unlock Pokémon or features. You enter them in a customizable quiz of the Pokémon Challenge, then complete the quiz. Here are the European codes, according to Poképédia.

The Pokédex 3D Pro.
CodeEffectHow to use it
PHSKUTDFThe Genesect entryEdit the code of quiz 37, 38 or 39, then finish the quiz
TTQALFHNBoth Formes of Meloetta and the move Relic SongEnter the code in a customizable challenge, then complete the quiz
UJFPJGADThe Pokémon Challenge’s Hard modeEnter the gift code

Genesect arrived in the Pokédex 3D Pro on January 17, 2013.