What are some good piano heavy metal scales and hard rock scales?
Yes, I know about the pentatonic,blues,harmonic and Phrygian scale. I need some more heavy metal scale which are unique and dark
For metal, I like to use a combination of different scales, including the pentatonic, blues, aeolian, dorian and harmonic minor. Diminished runs are often used, but can sound cliche at times. Try a half-whole scale (half tone followed by a whole tone, or opposite) for a unique vibe, or try to create your own scale using different numbers of notes. (Like an 8 or 9 tone scale)
I would also recommend doing a LOT of listening, particularly to the guitar parts of music you enjoy, and even to other types of music to inspire new ideas. Try some Jazz runs, or maybe some blues, then modify them to suite your style!
Good Luck