The Overworld Demo is the Demo in which the custom Overworld graphics are inserted, in this demo, none of the levels work right because all of the custom sprites were removed.

This and every newer demo are missing the sprites, so each one only has a few playable levels (the ones with only a few or no custom sprites, or the level the demo is supposed to show).

It's the prequel to the FF6 Demo and the sequel to the Demo 7.5.