Lux vs Swain

Start with Light Binding (Q), then Lucent Singularity (E) and Final Spark (R) before detonating the singularity: the root makes sure everything hits.

Slip in an auto after each spell that hits: it triggers Illumination (passive) for extra magic damage, and Final Spark (R) triggers it too.

Cast Lucent Singularity (E) into a brush before walking in: the area is revealed, and a hidden enemy would be slowed.

Cast Prismatic Barrier (W) through as many allies as you can: the wand shields them on the way out, then again on the way back.

Cast Final Spark (R) to clear a wave or secure an objective: it only has a 60 to 40 second cooldown, depending on rank.

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.