Fiora vs Master Yi

Position to hit the Duelist's Dance (passive) Vital: each Vital you hit heals you and gives you move speed.

Cast Lunge (Q) on the Vital's side: the strike prioritizes Vitals, and hitting an enemy lowers its cooldown.

Save Riposte (W) for enemy CC: it parries damage and effects for a moment, and if it parries an immobilizing effect, your stab stuns the first champion hit.

Hit the four Grand Challenge (R) Vitals by circling your target: if you hit them all in time, or they die after the first, you heal nearby allies.

Against Highlander (R), don't run alone: regroup with your team, because he gains speed and ignores slows.

If you have CC other than a slow, land it right after Alpha Strike (Q): during the strike, he's untargetable, and Highlander (R) ignores slows.

If you have CC, interrupt Meditate (W): he channels it to heal, more at low health, and to reduce the damage he takes.

Put pressure on his jungle early on: Master Yi is strongest once he has his items, and each stolen camp delays him.