Gangplank vs Nasus

Build a chain with Powder Keg (E): detonate the keg farthest from your opponent, and each keg whose area touches the previous one explodes too, all the way to them.

Last-hit minions and pop kegs with Parrrley (Q): a kill with the shot gives bonus gold, and so does a kill from a keg it sets off.

Save Remove Scurvy (W) for a key CC rather than for healing: it cleanses all CC on you, on a 22 to 14 second cooldown.

Cast Cannon Barrage (R) anywhere on the map to help a fight or cover an objective: each wave of cannonballs slows and damages in the area.

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.