Swain’s build depends on multiple variables. He is quite versatile so you can build a lot of different items on him.
Malignance is a perfect pick for Swain, this new item is designed for select few and Swain is one of them. The Ability Ultimate Haste combined with the ultimate burn makes Swain a legitimate FIRE BIRD DEMON. The Lost Chapter Build path allows you to prioritise this over Liandries.
Another great buy in Season 14 is Shadowflame. It works tremendously well when combod with Void staff as it offers a fantastic amount of burst while playing aggressive through a Hextech Alternator buy. This is usually combod that with a more AP heavy playstyle rather than tanky!
Sorcerer's Shoes give you extra pen and movement speed. Penetration is so important on Mages including Swain. It is also very good versus tanky team comps. If the enemy has lots of CC or lots of AP champions, Mercury's Treads. As Swain is pretty immobile and prone to CC, this item will give magic resistance and reduce the duration of major CC tools.
Rylai's Crystal Scepter is a great defensive item that is awesome on Swain, especially combod with his Ult. It is good on Swain because it increases his survivability which should help him stay alive in team fights: he can kite, slow and generally be a pain from when this is built. Rylai's Crystal Scepter is a cheap item that can be significantly under appreciated and overlooked. It synergises well with your kit and allows you to heavily slow the enemies which can help you catch up to them.
For your final item, you should go Rabadon's Deathcap. It will heavily increase your AP thanks to the raw and Passive stats it provides. In the late game, it will also heavily increase your damage output and make you a real threat in late-game fights.
In Season 14 Liandry's Torment is still a standard pick for Swain as it falls into his kit quite well, the constant poke and ease of procing it means that he can get a huge power spike from this item alone! This works tremendously well on Swain primarily due to his Ultimate and Conqueror combos. The early Haunting Guise fromt the build path significantly helps Swains early game. The downfall is that the new Liandrys doesn't have a mana orientated build path.
Ravenous Flock is Swain’s Passive
P - Swain can collect soul fragments from Vision of Empire, Nevermore and enemy champion deaths. These Souls restore % max health thats dependant on the level, this also permanently grants Swain 12 max health. This passive is fantastic as it helps Swain scale well into the late game alongside complimentiny his playstyle.
Death's Hand is Swain’s Q
Q - Swain deals damage in a cone. Enemies can be hit by multiple bolts and take bonus damage from his Death's Hand. Swain’s Death's Hand goes through minions and will be his primary tool to poke the enemy down in the lane..
Vision of Empire is Swain’s W
W - Summons an eye at a target location that grants vision for 1.5 seconds. It explodes after a short period of time, dealing damage and slowing the target. Your Vision of Empire will have a soul fragment ripped from them. As your Vision of Empire grants vision, it is good to use your Vision of Empire to check unwarded bushes for enemies rather than face checking them..
Nevermove is Swain’s E
E - Swain throws out a wave that deals damage to all enemies it passes through. Once it reaches the maximum distance, the wave returns to him. The first enemy it comes into contact with will take damage and be rooted briefly.
Demonic Ascension is Swain’s Ultimate
R - Swain becomes a demon for 12 seconds where he gains max health and doubles the health collected from soul fragments. While active, he drains health from nearby enemies (deals damage to them) and heals himself. After a brief delay, Swain can recast this ability which deals a considerable amount of damage to all enemies in the area of effect.
My preferred Rune setup for Swain:
Swain takes Conqueror as its keystone. There are many different options for Swain, but it depends on the lane you’re playing him in and your play style. Conqueror suits my Swain playstyle very well.
Conqueror is a good Rune on Swain. He can get stacks really easily, and the extra damage will be very beneficial when going for trades with the enemy. He can keep this rune stacked in team fights too.
Presence of Mind will offer you a lot of extra sustain throughout the game. One of Swain’s biggest issues is his lack of mana. This Rune will help you alot throughout the game.
Legend: Tenacity is a great Rune for a lot of champions, in particular, it is great on Swain. As Swain needs to get into the fight in order to deal damage with his Demonic Ascension, the extra tenacity will make it easier for him to get in and get onto the enemy.
Coup de Grace is a Rune that will help you execute enemies. Coup de Grace allows you to deal increased damage to enemies that are below 40% health. It will help you finish off targets.
For your secondary rune tree, go Sorcery with Manaflow Band and Transcendence. Manaflow Band offers you more mana which helps you throughout the game (again, this helps with his mana problems). Transcendence gives you more ability haste which allows you to use your abilities more frequently.
PROS & CONS
Pros
★ Very versatile champion. It can be built full damage or off-tank.
★ Although this guide only focused on Swain in 1 role, he can be played in multiple positions.
★ Lots of AOE damage thanks to his Demonic Ascension.
★ Great in team fights with his Ultimate Demonic Ascension.
★ Good pick potential thanks to his Passive and Nevermove.
★ His Vision of Empire can be used to scout unwarded bushes, which can save his life.
★ Good sustain in lane, especially post 6 with his Demonic Ascension.
★ Free health and tanky stats thanks to his Passive.
Cons
★ Mana dependent.
★ Has severe mana issues. You can reduce these issues by taking the Runes suggested in this guide.
★ Immobile and squishy, especially in the early game.
★ His Nevermove can be hard to hit.
★ Healing reduction is great versus Swain. It makes his Ultimate Demonic Ascension less potent.
★ Swain heavily relies on Zhonya's Hourglass in the mid and late game.