Ornn vs Cho'Gath

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.

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.