Lillia vs Master Yi

Hit with the edge of Blooming Blows (Q), not the center: only the outer edge adds true damage.

Hit enemies with your spells and keep your distance: Blooming Blows (Q) gives you a stack of move speed on each hit, enough to kite and dodge.

Start the fight from range with Swirlseed (E): it damages, slows and reveals, and if it hits nothing, it rolls on to the first enemy or wall.

Before Lilting Lullaby (R), hit as many enemies as you can: Dream-Laden Bough (passive) marks every target of your spells, and only marked ones fall asleep.

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.