Nautilus vs Swain

Aim Dredge Line (Q) at their carry: you and your target are pulled toward each other, and they're briefly stunned.

After Dredge Line (Q), land an auto right away: Staggering Blow (passive) roots the target after the stun, giving your ADC time to arrive.

In teamfights, hit a new target whenever you can: your first auto on each target triggers Staggering Blow (passive) and briefly roots them.

Cast Depth Charge (R) on their backline carry: every enemy the shockwave crosses along the way also takes a knock-up and a stun.

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.