Ornn vs Nasus

Cast Volcanic Rupture (Q) behind your target, then Searing Charge (E) into the pillar: when you hit that terrain, enemies around you take a knock-up.

Cast Bellows Breath (W) before your trade: nothing stops you during the breath, and the final burst of flame makes the target brittle, so your next auto knocks them back.

Recast Call of the Forge God (R) to ram the elemental: redirected, it knocks the first champion it hits into the air, then the next ones, and makes them brittle again.

Create masterwork items for your allies as soon as you can: Living Forge (passive) upgrades their items too, not just yours.

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.