Lee Sin vs Master Yi

For the Insec, land Sonic Wave (Q), reach the target, ward behind them and jump to it with Safeguard (W): Dragon's Rage (R) kicks them toward your team.

Wait until your target has lost health before casting Resonating Strike (Q): its damage scales with missing health, and you have 3 seconds to cast it.

Cast Safeguard (W) on an ally, minions included, or on a ward to dodge or escape: it has a 7-second cooldown and also shields the targeted allied champion.

Look for invades, ganks and objectives early on: Lee Sin is strongest early, and his impact drops once the others have their items.

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.