The Demon Fox rewards patient spacing, quick dodge timing and steady ranged damage more than risky close-range burst attacks.
Strategy
Circle the arena and wait for the boss to finish its charge pattern before committing damage. If your durability is low, reset distance after every short combo and avoid standing directly in front of the boss.
Keep the boss near the outer lane.
Attack only after the charge animation ends.
Use mobility to reset spacing, not to start every combo.