Supertonic: The supertonic is the second degree of a major or minor scale. In the key of C major, D would be the supertonic.
Mediant: The mediant is the third degree of a major or minor scale. In the key of C major, E would be the mediant.
Diminished Fifth: A diminished fifth is an interval consisting of six half steps (or three whole steps). It creates a dissonant and tense sound, often associated with horror movies or suspenseful moments in music.