Kha'Zix vs Rammus

Jump on an isolated target with Leap (E), then Taste Their Fear (Q): with no ally nearby, Unseen Threat (passive) marks them and the spell hits much harder.

In teamfights, cast Void Assault (R) to vanish and reposition: the invisibility triggers Unseen Threat (passive), and your next auto damages and slows.

Detonate Void Spike (W) close to you in the jungle or in teamfights: you heal if you're inside the explosion area.

Pick your evolutions to fit the game: evolved Leap (E) resets on each takedown, evolved Taste Their Fear (Q) gains range and a lower cooldown on isolated targets.

Stay behind your minions: Powerball (Q) stops on the first enemy it collides with, minions included.

If you deal magic damage, lean on it in trades when Defensive Ball Curl (W) is on cooldown: without it, his resistances drop to those of an ordinary tank.

If you're ranged, don't let him reach melee range when Frenzying Taunt (E) is ready: its range is short, and it forces you to attack him.

Get out of the Soaring Slam (R) area fast: aftershocks repeat the slow there, and if cast during Powerball (Q), it adds a knock-up in the center.

Don't attack during Defensive Ball Curl (W): each auto returns magic damage to you, and he gains armor and magic resist.