Rengar vs Master Yi

Fight near brush: from a brush, Unseen Predator (passive) makes your next auto leap onto the enemy.

Cast Battle Roar (W) right after taking damage in a trade: it heals you for part of the damage taken in the last few seconds.

At max Ferocity, pick your empowered spell: Savagery (Q) for damage, Battle Roar (W) to break free of CC, Bola Strike (E) to root.

Cast Thrill of the Hunt (R) to find an isolated carry: it reveals the nearest enemy champion, then camouflages you and lets you leap without brush.

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.