Kha'Zix vs Cho'Gath

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.

Keep moving against him: Rupture (Q) strikes an area on the ground, and an enemy standing still takes a knock-up, damage and a slow.

Punish him when he goes for last hits: Carnivore (passive) restores health and mana for each unit he kills, and he lasts a long time in lane if you let him farm.

If you have range, keep your distance: his kit has no dash, only the slows from Rupture (Q) and Vorpal Spikes (E).

Don't stay in melee range at low health when Feast (R) is up: its true damage ignores your resistances, even if you're a tank.