Sett vs Master Yi

Start your trades with Knuckle Down (Q): you rush toward your target, and your next two autos deal bonus damage based on their max health.

Cast Haymaker (W) right after taking damage: the stored Grit gives you a shield and extra damage, dealt as true damage in the center of the punch.

Don't back too early at low health: Pit Grit (passive) increases your health regen based on your missing health.

Stand between two enemies before Facebreaker (E): grabbed from both sides, they're stunned, otherwise only slowed.

Grab their tank with The Show Stopper (R) and slam them onto their carries: the damage around the impact depends on the bonus health of the target you grab.

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.