D-1

D-1 can refer to the following:
 * World D-1 from Super Mario Bros.: The Lost Levels.
 * Cold Case, mission D-1 from Luigi's Mansion: Dark Moon.
 * Level 1-1 from Mario vs. Donkey Kong: Tipping Stars, labelled "Level D-1" in the Mario vs. Donkey Kong tech demo.

D-1