Kayn vs Xin Zhao

Take Rhaast against a tanky team, Shadow Assassin against squishy targets: The Darkin Scythe (passive) gives one healing, the other bonus damage at the start of fights.

Gank through walls with Shadow Step (E): you move through terrain faster, and you heal when you first enter it.

To dodge a burst, cast Umbral Trespass (R) on a champion you just hit: inside, you're untargetable while your spells come back up.

As Rhaast, hit as many champions as you can with your spells: The Darkin Scythe (passive) heals you for part of the ability damage they take.

Get out of the line of the Wind Becomes Lightning (W) thrust: it slows you and marks you as Challenged, which extends the range of Audacious Charge (E) on you.

If you have CC, use it during Three Talon Strike (Q): without his three autos, there's no knock-up, and his other cooldowns don't go down.

After Audacious Charge (E), keep your distance: it's his only dash to get back on you, and without it he has to walk up to you.

After Crescent Guard (R), don't hit him from range: for a moment, he ignores damage from outside the swept zone. Back off, or hit him from inside it.

If you survive his first minutes, play for time: Xin Zhao is strongest early on, through his ganks and skirmishes.