Zed vs Jax

To kill, cast Death Mark (R), then Living Shadow (W), Shadow Slash (E) and Razor Shuriken (Q): with two shadows, you throw three shurikens.

Cast Death Mark (R) just as the enemy casts their decisive spell: during the dash, you're untargetable.

After Death Mark (R), save the recast to get out: you swap places with the shadow left at your starting point, far from the fight.

Save enough energy for a full combo rather than casting your spells for nothing: Living Shadow (W) refunds energy when you and your shadow hit the same target.

In teamfights, go around the sides and save Death Mark (R) for an isolated target: going in from the front exposes you to the whole team's CC.

Take a short trade, then back off: Relentless Assault (passive) increases his attack speed with each consecutive auto.

During Counter Strike (E), back off instead of attacking: he dodges your autos, then stuns nearby enemies, dealing more damage per dodged auto.

Trade right after Counter Strike (E): it's both his defense and his only stun, and it has a 17 to 9 second cooldown.

In the late game, don't leave his split push unanswered: send someone to hold his lane, or force an objective on the other side of the map.