Syndra vs Swain

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.

Get out of the Nevermove (E) path as it comes back: it only roots on its return to Swain, then he can pull each rooted champion to him.

Leave the area as soon as Vision of Empire (W) appears: it strikes and slows 1.5 seconds later, and each champion hit gives him a Soul Fragment.

During Demonic Ascension (R), back off and hit from range if you can: he only drains nearby enemies, and his form ends when he stops draining.

If you have Grievous Wounds, apply it during Demonic Ascension (R): the drain heals him every second, and that healing keeps him alive.