To coincide with this weekends Pokemon Go Fest, legendary Pokemon will start being seen in the world. According to the official site, players can start looking for these elusive creatures on Saturday, July 22nd IF the folks in Chicago can defeat the very first one. Once done, Legendary Eggs will appear in gyms around the world the next day.
If the first Legendary Pokémon is defeated in Chicago, it will then begin to appear in Legendary Eggs at Gyms around the world. If you and your team are able to defeat the Legendary Pokémon, each of you will then have the chance to catch it! Once caught, you can use the Pokémon like you would any other Pokémon, except Legendary Pokémon cannot be assigned to defend a Gym. Don't hesitate to join a Raid Battle to catch this awesome Pokémon while you can!
Starting July 22nd, players should work to catch as many Pokemon as possible assist their team while those in Chicago are unlocking other neat prizes for the entire community.
You can read the full update on the Pokemon Go site.