Rek'Sai vs Cho'Gath

Save Furious Bite (E) for when your Fury bar is full: the bite then deals true damage.

Come out of the ground with Un-burrow (W) under your target: they and nearby enemies take a knock-up, so you can engage or interrupt a channel.

Cast Void Rush (R) on an enemy you damaged in the last few seconds: untargetable, then unstoppable, you lunge at them, and your Un-burrow (W) comes back.

Cast Burrow (W) before crossing the map: your Tremor Sense reveals to your team nearby enemies who move unseen.

Dig with Tunnel (E) near lanes to gank and on your escape routes: each tunnel lasts and can be reused, but an enemy standing on an entrance destroys it.

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.