Syndra vs Yasuo

Place Dark Sphere (Q) between you and your target, then cast Scatter the Weak (E): the sphere you push stuns the enemies it hits.

After landing Force of Will (W), follow up right away with Dark Sphere (Q): the target is slowed and has a hard time dodging it.

Poke with Dark Sphere (Q) from level 1: it has 800 range, its cooldown is only 7 seconds, and each rank of your ult lowers it further.

Hit enemies whenever you can: Transcendent (passive) gives you Splinters of Wrath for every level and every hit, and each threshold upgrades one of your spells.

Place several spheres before Unleashed Power (R): the ult launches the 3 orbiting you at your target, plus up to 4 more nearby.

Hit him with a cheap attack to trigger the Way of the Wanderer (passive) shield, then start the real trade: otherwise, it absorbs your best damage.

If you have projectiles, save them for after Wind Wall (W): it blocks them all for 4 seconds, on a 25 to 17 second cooldown. Other spells go through it.

Don't stand right behind your minions: each one gives him a target for Sweeping Blade (E), and he gets closer to you with every dash.

Get out of the line of his whirlwind, the third Steel Tempest (Q): without a knock-up, he can't cast Last Breath (R).

Judge his threat by his crit items more than his level: Way of the Wanderer (passive) raises his critical strike chance, so each crit item does more for him.