Rayquaza, the flagship Pokemon of Pokemon Emerald, is now available in Pokemon Go. According to a recent blog post by Niantic, the Legendary Pokemon is available from now until March 16. The Raid Battle will presumably close at 1:00 p.m. PST / 4:00 p.m. EST on that day as those were the closing times for the previous two Legendary Raid Battles.
The last Legendary Raid Battle involved Kyogre, the flagship Pokemon of Pokemon Sapphire. The Legendary Pokemon is actually leaving on February 14, 2018 at 1:00 p.m. PST / 4:00 p.m. EST, giving you a few more days to catch it.
Rayquaza released on February 9 along with brand new Pokemon from generation three. The 20 new Pokemon coming to the game according to The Silph Road subreddit are Castform, Swablu, Altaria, Surskit, Masquerain, Bagon, Shelgon, Salamance, Tailow, Swellow, Volbeat, Illumise, Beldum, Metang, Metagross, Tropius, Wingull, Pelipper, and Chimecho. The remaining gen three Pokemon who are not currently available are Nincada, Ninjask, Shedinja, Kecleon, Clamperl, Huntail, Gorebyss, Regirock, Regie, Registeel, Latias, Latios, Jirachi, and Deoxys.
Volbeat are exclusive to Europe and Asia-Pacific regions; Illumise are exclusive to the Americas and Africa; and Tropius are exclusive to Africa as well as parts of the Mediterranean and the Middle East. Plusle and Minun are no longer region exclusives and are available globally.
Castform changes form depending on the weather. Normal form is encountered in cloudy and partly cloudy weather; sunny form in sunny/clear and windy weather; rainy form in rainy weather; and snowy form in snowy and foggy weather.
The Pokemon Swablu, Snorunt, Dewgong, Jynx, Azumarill, Piloswine, Feraligatr, and Rayquaza have been added as Raid Bosses.
According to a blog post by Niantic, gen three Pokemon will take over wild encounters until February 13. New Special Boxes are also available to purchase in the in-game store until February 23. Lure Modules will have their duration extended to six hours until February 23.