https://www.gamespot.com/articles/pokemon-lets-go-pikachu-and-eevees-legendary-pokem/1100-6461876/

The Pokemon Company has shared another new trailer for Let's Go, Pikachu and Let's Go, Eevee. While the last video focused on Celadon City and some of the new attacks your partner Pokemon can learn, the one above provides another look at the Go Park--the facility where you'll transfer monsters from Pokemon Go--as well as the Legendary birds Articuno, Zapdos, and Moltres.

As hinted at in a previous trailer, while the Let's Go games don't feature wild Pokemon battles, you will be able to fight the Legendary birds. Just as in Pokemon Go, however, you'll only earn a chance to capture them if you first defeat them in battle. There appears to be another caveat; in the screenshot below, you can see a timer in the upper lefthand corner of the screen, suggesting you'll only have a set amount of time to defeat the Legendary birds.