Giovanni's Shadow Zapdos
In the month of December, you can find and battle Giovanni, the boss of Team GO Rocket, to rescue Shadow Zapdos.
Tracking down Giovanni requires completing the Special Research ‘A Troubling Development’ to obtain the Super Rocket Radar. The Super Rocket Radar will allow you to find potential PokéStop where Giovanni is hiding out. Some of them might be Decoy Grunts, so it might not be a simple task. After you challenge and defeat him, you’ll have the opportunity to capture a Shadow Legendary. This month, he will have Shadow Zapdos in his party.