Naafiri vs Master Yi

Recast Darkin Daggers (Q) on a target that's already bleeding: the second dagger deals the rest of the bleed plus damage based on their missing health, and heals you.

When your pack has taken hits, cast Eviscerate (E): your packmates come back to you at full health.

Cast The Call of the Pack (W) just before you engage: you're briefly untargetable, your pack grows, and you gain AD and move speed.

Push your wave, then roam toward an isolated champion: with Hounds' Pursuit (R), you and your pack dash onto them, and a takedown lets you recast it.

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.