If you manage to beat all three, you will get to fight Team GO Rocket leader Giovanni and net yourself the new legendary shadow Pokémon Articuno to aid you in your quest of catching them all.
Tips: This is a pretty easy first step. You'll find Team GO Rocket Grunts as you walk around spinning PokeStops. You'll know they're there because the PokeStop is noticeably darker and quivering.
Niantic is also bolstering the business side of its platform by letting small or medium size businesses schedule events such as Pokemon Go "raids" where players rally together to battle tough in-game adversaries.
Finally, Niantic shared a general update on how "the company is building towards the future of augmented reality experiences by mapping, sharing and understanding reality", such as the Niantic Wayfarer program - a shared AR multiplayer experience for Pokémon Go called Buddy Adventure (working title) - and new developments towards "their revolutionary computer vision technology to help create more immersive experiences through occlusion". You can then use these Mysterious Components to assemble a Rocket Radar.
With the Rocket Radar, you'll be able to detect the hideouts of the Team Go Rocket leaders.
Rocket Radars at the ready! If you lose a battle against the Leader, you can challenge them again until the Leader Hideout disappears from the map. It's important to note that other players, even if they have a Rocket Radar or Super Rocket Radar, won't be able to assist you when you take on the Team Go Rocket leaders. Only players level eight and above can get Mysterious Components and take on the Leaders, according to the website. Completing the Looming in the Shadows tasks will eventually unlock the Super Rocket Radar.
There are a few hoops you'll have to jump through to add the new legendary shadow Pokemon to your team.
This confirms that the Legendary Shadow Birds will make their debut, most probably we will battle them as part of the Looming in Shadows Special Research stage 6/6, and that's when we will see Giovanni.