BAD MARIO FANGAME IDEA; You go everywhere. So you start our basic, with Mario and Luigi, but from the FIRST LEVEL, you have access to a second world that lets you access TWO MORE worlds. They're the Beanbean Kingdom, and you go there to fly to either The Sunshine Archipelago or Dinosaur Land. Both of the original paths lead to Bowser territory, and then you get transported to the Lost Kingdom, Cave Story Labrinth style, then go to the three Sarasaland worlds.
This isn't even all of the stuff in it.
and put it on scratch.