Super Smash Bros. Ultimate will give you Partner Pikachu/Eevee Spirits with Pokemon: Let’s Go save data
Super Smash Bros. Ultimate will give out a small bonus if you own Pokemon: Let’s Go. If you have Pikachu save data, you’ll be provided with the Partner Pikachu Spirit. Eevee save data will net you the Partner Eevee Spirit.
Fortunately, both can be accessed normally as well. Complete challenges and they’ll be yours, even without save data.