Raid Boss

A Raid Boss or Boss Pokémon is an extremely powerful Pokémon that has very high CP. It hatches from a egg which appears atop a Gym upon the beginning of the Raid Battle. A countdown will display the time until the egg hatches and the battle begins.

Details
Upon using a Raid Pass to join the battle, the Trainer and up to 19 other Trainers work together to defeat the Raid Boss. If a Raid Boss is successfully defeated within the three-minute time limit, or five-minute time limit for Legendary Raids, those Trainers have the chance to catch a decently powerful Pokémon of their own. The captured Pokémon does not necessarily have the same moves as the Raid Boss.

A Raid Boss can battled as many times as possible before it is either defeated or the 45-minute time limit expires.

List of Raid Bosses
There are a limited number of Pokémon that can be possible Raid Bosses at the same time. The pool of available Raid Boss Pokémon have been changing since the feature release. Additionally, in past events, there have been exclusive Raid Bosses that cannot normally be encountered in Raid Battles.

Raid Boss CP formula
The formula is identical to the traditional CP Formula; except the stamina and CP scalar portion in the divisor are replaced with a tier scalar which represents the Raid Boss's HP and the IVs for attack and defense are fixed to 15 (maximum IV value).

$${BCP = \frac{(Base Atk + 15) ~ \times ~ \sqrt{Base Def + 15} ~ \times ~ \sqrt{TierScalar}}{10}}$$

Where   is:
 * Tier 1:  
 * Tier 2:  
 * Tier 3:  
 * Tier 4:  
 * Tier 5:  
 * Tier 6 (marked as 5):  

Trivia

 * The Raid Boss icon is based off of Rhydon's face — who was the first Pokémon designed and programmed into the original game. There are also various Rhydon statutes that can be found throughout the game as well.
 * On November, 2017, the raid bosses were rotated for the first time.
 * During Pokémon GO Park and Pokémon GO Stadium event in Yokohama, for the first time in game, there were several event-exclusive Raid Boss Pokémon available.
 * Pokémon such as Meowth, Pikachu, Wobbuffet, Ursaring, Houndoom and few others were available as Raid Bosses on 4th tier level.
 * Before January, 2019, the stamina of tier 3 to 6 Raid Bosses were 3,000, 7,500, 12,500 and 18,750 respectively.
 * Mewtwo in normal Raid Battle and Darkrai in Halloween 2019 are the only tier 6 Raid Bosses, with buffed HP and CP.