Rammus vs Cho'Gath

Engage with Powerball (Q): your speed builds while you roll, and the impact knocks back and slows enemies around your target.

Cast Defensive Ball Curl (W) when you're being hit by autos: you gain armor and magic resist, and each attack returns magic damage to its attacker.

Cast Frenzying Taunt (E) during Defensive Ball Curl (W): forced to attack you, your target takes damage with every auto.

Cast Soaring Slam (R) during Powerball (Q): enemies in the center of the area also take a knock-up, and your speed extends the leap's range.

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.