Nami vs Swain

Cast Aqua Prison (Q) on a slowed or immobile target, or where they're heading: the bubble lands in an area and stuns every enemy on impact.

Cast Tidecaller's Blessing (E) on your ADC just before they trade: their next autos and abilities slow and deal bonus magic damage.

Cast Ebb and Flow (W) so it bounces from one champion to another: it heals each ally, damages each enemy, and only hits the same champion once.

Cast Tidal Wave (R) to engage or to break an enemy engage: enemies hit take a knock-up and a slow, which lasts longer on those farther away.

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.