Raid Battle

A Raid Battle is a special event that takes place within a Gym 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.

They seem to only run between 8AM (starting time) and 10PM local time.

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.

History

 * 23rd June - Raids were open being available for players level 35 and above
 * 23rd June - Raids were made available for players level 31 and above
 * 23rd June - Raids were made available for players level 28 and above
 * 24th June - Raids were made available for players level 25 and above
 * 26th June - Raids were made available for players level 20 and above
 * 1st July - Raids were made available for players level 5 and above