piano scale
D♭ Phrygian
Minor with a flattened second — the half step right above the tonic is the whole character.
The same sounds spelled from the other side are C♯ Phrygian.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
What is true of it
D♭ Phrygian is D♭, E♭♭, F♭, G♭, A♭, B♭♭ and C♭, and back to D♭.
Its steps are H – W – W – W – H – W – W, where W is a whole step and H a half.
Written correctly it needs 9 alterations, E♭♭ and B♭♭ among them. That is what the letters force, and it is also why nobody writes music in this key: the same notes spelled from the other side are easier to read.
On the same tonic, D♭ natural minor differs from it by exactly one note.
Chords made only of these notes
Found by testing every chord in the catalogue against these 7 sounds, not chosen.