All three creatures will roll out today (or most likely tomorrow in the UK) and individually appear in specific regions for one month at a time. Raikou will only be available in the Americas, Entei will only be available in Europe and Africa, and Suicune will only be available in Asia.
From today, August 31, until September 30, players will be able to find one of the three Pokémon on different continents.
Developer Niantic is also testing the new Exclusive Raid Battle system it debuted in Japan earlier this month.
The new Legendary is likely going to be one of the hardest to battle and catch, so having these small tweaks to make the process that little bit easier could prove decisive. It's now thought that certain Pokemon will be exclusive to the Ex Raids so players will only be able to capture them by completing one of these events.
Omastar, Vaporeon, Golem, and Rhydon are the best Pokemon to use to counter Entei, with Feraligatr and Gyarados acting as solid secondary options.
Pokémon GO is available for Android and Apple iOS devices.
Added the ability to view the number of Trainers entered, and preparing, for a Raid Battle before using a Raid Pass.
Gyms where raids are about to begin are indicated with an egg.
Players go through five different levels during raids in Pokemon Go. These rare Pokemon will join the likes of the legendaries already in the game which gives us pretty much every legendary available from generations one and two.