Nasus vs Cho'Gath

Last-hit minions with Siphoning Strike (Q): each kill with the spell permanently increases its damage, by more on large minions and champions.

In teamfights, cast Wither (W) on their carry: the slow grows stronger over the spell's duration and also reduces their attack speed.

Cast Fury of the Sands (R) as you enter a teamfight: for 15 seconds, you gain health and resistances, damage nearby enemies, and Siphoning Strike (Q) comes back faster.

Early on, farm rather than force trades: Siphoning Strike (Q) stacks are permanent, and every minion you last-hit makes you stronger later.

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.