Pokémon GO developer Niantic has fully detailed the recently-added Lucky Pokémon feature. There is now a chance that Pokémon can become sparkly Lucky Pokémon when traded. Lucky Pokémon require less Stardust to power up, which means they can reach a higher CP much faster than other Pokémon.
Lucky Pokémon can be detected by the Pokédex. In addition, the longer the Pokémon spends inside a Trainer’s Pokémon storage, the higher the chance of them becoming Lucky Pokémon when they are traded. With the discovery of Lucky Pokémon, Gifts also can include special new surprises. Trainers who send Gifts to friends will now receive XP for doing so and Gifts also have a chance of containing Stardust.