Let's identify the compositional techniques used by Shiho Fujii and
Mahito Yokota in the New Super Mario Bros. U - Ghost House Theme! Please refer to the following video:
The theme begins in a minor. However, the bass line begins on the 5th instead of the root, making the tonality unstable. Futhermore, the many dimished chords create dissonance and undermine the key of a minor. These harmonic changes contribute to the spookiness of the Ghost House Level where the level can be like a maze. Also, Mario open doors to go from one room to the next. The many different sections of music represent different parts of the maze. At the completion of the level, Mario says, "This way!" which agrees with the notion that the Ghost House level is like a labryinth.
The P-Switch music contains diminution of the theme, a rhythmic accelerando, and a chromatic ascending line. These effects relate to the gameplay where blue coins briefly appear for about 9 seconds. There is a certain urgency for the player to take action once Mario has stepped on a P-switch.