Raid Battle

Raid Battles are an upcoming feature in Pokémon GO.

Background
A Raid Battle is a cooperative gameplay experience that encourages Trainers to work with other Trainers to defeat an extremely powerful Pokémon known as the Raid Boss. Before a Raid Battle begins, all Pokémon assigned to the Gym will return to their owners, and a large Egg will appear atop the Gym. When the countdown above the Egg reaches zero, the Raid Boss will be revealed.

Raid Pass
Before a Trainer can battle the Raid Boss, they'll need a Raid Pass. Trainers can receive one free Raid Pass per day by visiting a Gym, but can only hold one at a time. A Premium Raid Pass may also be purchased from the in-game Shop.

Raid Boss
Upon using a Raid Pass to join the battle, the Trainer and up to 20 other Trainers work together to defeat the Raid Boss. If a Raid Boss is successfully defeated within the five-minute time limit, those Trainers have the chance to catch an extra powerful Pokémon of their own.

Rewards
After defeating a Raid Boss, Trainers receive a collection of rewards, including some new items obtained only by defeating a Raid Boss: Rare Candies, Golden Razz Berries, and Technical Machines.