If you trade a Pokémon that has spent any time inside Pokémon storage from July 2016 to August 2016—when Pokémon Go launched—that Pokémon is guaranteed to become a Lucky Pokémon.
Guaranteed Lucky Pokémon!
Get Lucky Pokémon in Pokémon GO when you trade with friends who played long ago.
September 05, 2018
Do you want more Lucky Pokémon? Now, when the right conditions are met, you can guarantee that Pokémon trades will result in Lucky Pokémon for both Trainers!
The nature of Lucky Pokémon remains the same—the longer a Pokémon spends inside a Trainer’s Pokémon storage, the better chance of it becoming a Lucky Pokémon when it’s traded. But starting in early September, if you trade a Pokémon that has spent any time inside Pokémon storage from July 2016 to August 2016—when Pokémon GO launched—that Pokémon is guaranteed to become a Lucky Pokémon. Also, either you or your friend must have discovered fewer than 10 Lucky Pokémon. And, from now on, all Lucky Pokémon that you get will be more powerful than before!
Now is the perfect time to invite old friends back into Pokémon GO and trade together to get stronger Pokémon!
Good luck, Trainers!
— Pokémon News
…Wanna play? Buy a 3DS.
That being said, click on Pokémon Go for everything you need to know about the game. 😀