Pokémon GO has announced a trait for captured Pokémon, “Lucky”, which dramatically (or entirely) reduce the amount of Stardust required to power them up. These Pokémon gain the Lucky trait when traded with friends and monsters who have been stored for longer amounts of time have a higher chance of gaining the trait.
The longer the Pokémon spends inside a Trainer’s Pokémon storage, the higher the chance of them becoming Lucky Pokémon when they are traded. Whether or not being in storage causes Pokémon to become Lucky Pokémon remains a mystery, but be sure to stay posted for more results from the professor’s research.
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! – Official Site
The official site has also mentioned exciting upgrades for trade-able Gifts as well, which now can reward Stardust, the currency for powering up Pokémon and trading them.
https://www.youtube.com/watch?v=STOPt43iEiE
Keep interacting with friends and let us know if you receive any of these Lucky Pokémon!