Flatbush
Flatbush is a community in the burrough of Brooklyn, in New York City. Despite Brooklyn being mentioned in the various TV shows, books, comics and in the movie, Flatbush was only ever mentioned on The Super Mario Bros. Super Show!.
Flatbush is the neighborhood where Mario and Luigi grew up, and is also where they set up Mario Brothers Plumbing. As such, all the live-action segments take place in Flatbush. A famous street in Flatbush is the eponymously named "Flatbush Avenue".
During return trips to Brooklyn, it is unknown if the neighborhood of Flatbush is actually visited or not. Salvador Drainado claimed to be from Flatbush, and managed to return home after being stuck in the Mushroom World for thirteen years in "Brooklyn Bound / Cher's Poochie".
In "Flatbush Koopa / Opera", King Koopa attempted to take over all of Brooklyn. Upon seeing Mario and Luigi, he threatened to flatten them worse than he was going to flatten Flatbush. However, his takeover was ultimately foiled.