Timmy & Tommy
In the early Animal Crossing games, Timmy and Tommy Nook were Tom Nook's nephews, who assist him in running Nookington's, the largest upgrade to his store. However, starting in New Leaf, they completely take over the shop while their uncle runs a real estate agency. Their role in Villager's Final Smash likely references them being Tom Nook's assistants in the first three games.
In Smash Tour
Timmy & Tommy are a blue Tour item that changes nearby items into other, random items.
The twins also appear as a Master Spirit. They run one of the shops in Adventure Mode: World of Light.