Udyr vs Master Yi

Swap stances every two autos: after each spell, Bridge Between (passive) gives attack speed to your next two attacks.

Switch to Iron Mantle (W) when you're taking damage: you gain a shield, and your next two autos heal you. Once awakened, it also heals you over time.

In Blazing Stampede (E), each auto makes you dash to your target and stuns them. Switch targets to stun several: the same target can't be stunned again for a while.

To engage into a team full of CC, awaken Blazing Stampede (E) by recasting it: you become immune to immobilizing effects and gain move speed.

Cast Wingborne Storm (R) while running at the enemies: every second, it damages and slows everyone around you.

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.