Zac vs Cho'Gath

After Stretching Strikes (Q) on one enemy, hit a second enemy with your auto: you fling them into each other, and if they collide, they and those nearby take damage.

Pick up the chunks of Goo you shed when your spells hit: Cell Division (passive) heals you for each one, and Unstable Matter (W) comes back 1 second sooner.

Charge Elastic Slingshot (E) from the fog of war: the enemy has less time to react, and the longer the charge, the longer the knock-up on landing.

Cast Let's Bounce! (R) into the heart of their team: the first bounce knocks back each enemy hit, the following ones slow them, and you can cast Unstable Matter (W) at the same time.

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.