Your Win Condition
Force an all-in when she misses Q. Outrun her with boots.
General Strategy
If she lands Q (poison), she wins in melee range because she can spam E. Rush upgraded boots (Merc Treads recommended) early, as Cassiopeia cannot buy boots, giving Darius a huge movement speed advantage that helps land the pull. Run D Shield and Second Wind to sustain her poke. If you are capable of dodging everything, going Sorcery runes can provide extra move speed.
Trading Patterns
Once she misses Q, run to her, pull her, and fight. When you fight her close, she will use W (Miasma), which slows you, enabling her to land Q. Use Ghost to get as close as possible; if she casts W close to herself, its area is small, allowing you to walk outside of it and re-engage. Merc Treads reduce the duration of her ultimate's stun.
Wave Management
Their Win Condition
Landing Qs consistently. Using W (Miasma) to slow Darius and set up Qs and E spam. Utilizing ultimate R (Petrifying Gaze) for the stun.
