Zac vs Nasus

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.

Early on, take a trade whenever he steps up to last-hit a minion: each kill with Siphoning Strike (Q) increases its damage for the whole game.

Freeze the wave near your tower: to farm with Siphoning Strike (Q), he then has to step up and expose himself to ganks.

Once he hits level 6, don't engage during Fury of the Sands (R): for 15 seconds, he gains health and resistances, and his area damage scales with your max health.

In teamfights, if you're ranged, hit him while backing off: he has no dash, only Wither (W), a slow that grows stronger over time.