Tank Swain Build

General

1. You start with Guardian's Horn. Your #1 rush should be item that counters enemy team most (MR or Armor item). Get Jak'Sho as #2 item. Then adapt.
2. You will be more tanky later on, so play more carefully in the early game.
3. Triumph is better overall (heal + gold), but if you want to have easier time with your mana, go Presence of the Mind.
4. Guardian's Horn is a surprisingly good item for its price. You can keep it for very long time (or even have it as 6th item).
5. You need to adapt your items to the game. Enemy team heavy on AP? Buy MR. They heavy on AD? Buy Armor. You need some damage? Well buy that.
6. Remember to consume your Grasp of the Undying procs!

Champion

1. You can use Vision of Empire (W) to stop enemies taking portal (frost-gate). Time it well, and they will need to walk, and you will get the turret!
2. Vision of Empire (W) trick works even better with all DoTs effects (Liandry's Anguish and Demonic Embrace).
3. Enemies in your base? Use Demonic Ascension (R) before taking portal (frost-gate), this way you damage everyone on your way.
4. Did you just catch someone with your Nevermove (E)? Do not use second E right away, but use it at the very last moment for maximum CC.
5. After you catch someone with your Nevermove (E), you can set up Vision of Empire (W) for a certain hit.

Riot

1. If you're having trouble rooting an enemy with Nevermove, try throwing it at opponents when they are near their minions so the explosion surprises them.
2. While laning, try to use Death's Hand's piercing damage to damage opponents from a safe distance.
3. Vision of Empire is quite difficult to land on its own, look for skirmishes around the map where enemies may be distracted or crowd controlled so you can land it more easily.
4. Demonic Ascension may make Swain very hard to kill but he's pretty easy to get away from. Try building items that can slow opponents to keep them in range if their mobility is overwhelming.