Kha'Zix vs Bel'Veth

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.

Back off when she takes her true form with Endless Banquet (R): she gains health, range and attack speed, and with enough stacks, the form lasts until she dies.

Dodge Above and Below (W): if it hits you, you take a knock-up and her Void Surge (Q) in your direction is refreshed instantly.

If you're the lowest-health enemy near her, get out of Royal Maelstrom (E) range: every slash targets you, and she gains lifesteal and damage reduction.

Deny her large monsters and kills: Death in Lavender (passive) gives her permanent attack speed for each one.