Locrian mode is a mode of the major scale where you drop the 2nd, 3rd, 5th, 6th and 7th notes in the scale by a semitone, or one note (1, b2, b3, 4, b5, b6, b7).
For example:
C Major: C, D, E, F, G, A, B, C
C Locrian: C, C#, D#, F, F#, G# A#, C
Locrian is particularly challenging to compose in because its root chord is a tritone, super unstable
You can make it sound resolving by hammering home the root note or the tritone (in C Locrian that’d be either C or the chord C, D#, F#)
Most music composed in it is very tense, and that’s the easiest direction to go.
Attached below is a sequence with C Locrian, pull the scale up a semitone to get C# Locrian, and down a semitone to get B Locrian, and so on…

(legendary also beat me to it sorta, check out his sequence for all the Locrian scales)
For example:
C Major: C, D, E, F, G, A, B, C
C Locrian: C, C#, D#, F, F#, G# A#, C
Locrian is particularly challenging to compose in because its root chord is a tritone, super unstable
You can make it sound resolving by hammering home the root note or the tritone (in C Locrian that’d be either C or the chord C, D#, F#)
Most music composed in it is very tense, and that’s the easiest direction to go.
Attached below is a sequence with C Locrian, pull the scale up a semitone to get C# Locrian, and down a semitone to get B Locrian, and so on…
(legendary also beat me to it sorta, check out his sequence for all the Locrian scales)