During today's E3 Direct Presentation, Nintendo revealed a few more details regarding Pokemon: Let's Go, Pikachu! and Pokemon: Let's Go, Eevee! Most importantly, Mythical Pokemon like Mew cannot be obtained through normal means and are obtained through the additional Poke Ball Plus accessory. Details were also provided on other elements of the game, such as GO Park & Link Trading/Battles:
Here's the rundown from Nintendo regarding the Poke Ball Plus:
A new accessory, called Poké Ball Plus, comes with Mythical Pokémon, Mew and is sold separately from the games. Poké Ball Plus includes a pressable analog stick and button, so players can control the new games entirely with the accessory, if they want. Nintendo is announcing two bundles, in which players can get Pokémon: Let’s Go, Pikachu! or Pokémon: Let’s Go, Eevee! with one Poké Ball Plus at a suggested retail price of $99.99 each.
And here's more information from The Pokemon Company regarding Mythical Pokemon, GO Park, Candy Jar, and Link Trading/Battles:
Nintendo’s E3 2018 digital presentation included additional details about the Mythical Pokémon Mew, an incredibly rare Pokémon that cannot be encountered in regular gameplay in any of the Pokémon main series games. For Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee!, Mew will be available in the Poké Ball Plus, and players will be able to transfer it to their version of the new game. Each individually sold Poké Ball Plus will contain Mew, as will all the Poké Ball Plus accessories sold in special packs. Mew caught while playing Pokémon GO cannot be brought into Pokémon: Let’s Go, Pikachu! or Pokémon: Let’s Go, Eevee!
Additional game information was unveiled via the Nintendo Treehouse Live presentation at E3 2018 in Los Angeles, where Game Director Junichi Masuda from GAME FREAK gave a demonstration of the game. Various gameplay elements were shown, including parts of Viridian Forest and Pewter City, and a familiar face to Pokémon fans—Brock!
Other features of Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee! that were revealed today include:
GO Park—GO Park is enabled as a player progresses further in the game and will help players befriend Pokémon from Pokémon GO in Pokémon: Let’s Go, Pikachu! or Pokémon: Let’s Go, Eevee! This feature allows for Pokémon from Pokémon GO originally discovered in the Kanto region to be transferred to Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee! These Pokémon will then need to be caught with a Poké Ball. The player can interact with them in a whole new way in Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee!
Candy Jar—Players can use a variety of Candies to strengthen their Pokémon in a training system introduced in Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee! Later in the game, players will be able to send their Pokémon to Professor Oak to receive these Candies.
Link Trading and Battles—Players will be able to trade and engage in Single and Double Battles with other players online and via local wireless communication. Trading and battling online will require an active Nintendo Switch Online membership, a paid service launching this September.
Pokemon: Let's Go, Pikachu! and Pokemon: Let's Go! Eevee are scheduled to be released worldwide on November 16, 2018. You can find the announcement information here.