Swain. He has been one of the strongest midlane champions for a long time. He's hard to beat in lane, and he's an absolute monster late game. He's pretty adaptable as far as his item build goes, and he's pretty easy to pick up and learn. All things considered, Swain is a great choice to play in the midlane in any game. This guide will walk you through an effective way to build Swain through masteries, runes, item choies, a

Pros
-Naturally tankier than most AP mids
-Long Area of Effect snare
-Very good sustain
-Damage is persistent over time
-Skills are very easy to use
-Monstrous late game
-Hard to kill

Cons
-Very mana hungry with his ultimate
-Countered by Greivous Wound
-Have to be relatively close to deal full damage
-Kind of a pain to build his core items
-No gap closers or speed ups

For runes, I run Magic Penetration, Ability Power, Health, and Magic Resist. This way you will be maximizing your damage while remaining tanky enough in lane to bully your opponent. Most midlaners won't be able to stand toe to toe with Swain. He does good enough damage and shrugs off enough damage to call the shots in lane most of the time, and this rune page is set up to help highlight that.

Masteries are 21 Offense, 9 Defense. The standard ability power path in the offense tree is the way to go, maximizing your damage output. For the 9 points in defense, I put those towards sustainability and maximum health, to give you that extra beefiness that let's you take a few extra hits. Swain is slow, which means you'll be taking some hits, so having high health is a must.

Core Items

Rod of Ages: You will likely find this item suggested in every Swain guide, because it works picture perfect on him. It gives Health, Mana, and ability power, as well as the passive that heals you at every level up, which is great to help you stay in lane longer and rack up gold and experience. You should generally rush this before anything else.

Zhonya's Hourglass: A very good item on Swain. It brings great damage and some armor, which is nice, but the real star on top of the tree here is the items active. Activating this item will place your champion into stasis, which means he will be unable to be targetted or take any damage for 2.5 seconds. However, if your ultimate is on while you go into stasis, it continues to damage enemies around you and bring back health to you, and there will be nothing they can do about it. A great choice for Swain.

Athene's Unholy Grail: I wasn't 100% sure if it was right to call this a core item, but here we are. Swain suffers from mana issues, and this is the perfect item to counter that. It was recently buffed, and the mana regen now combines so perfectly with Swain's passive that it's hard to pass up on. If a 5v5 teamfight, you will gain almost 40% of your max mana back after a kill or assist, so you will be walking out of a finished fight with full mana. Also worth noting is the 20% cooldown reduction, which is always helpful. Add on top of that decent ability power and a dose of magic resist, and you've got a great item. (If the enemy does not have any ability power, or if there are several enemies that rely on health regeneration to be effective such as Volibear, Dr. Mundo, or Vladimir, replace this item with Morellonomicon).

Boot Options
9 times out of 10, you will be taking Sorceror's Shoes. Swain's here to do magic damage, and these are the boots that help you do that, with plus 15 magic penetration. On some occasions, however, you might end up wanting Mercury Treads instead. You would want those if the enemy is heavy on the AP side (I'm talking 3 or more AP champs) and/or they have a whole lot of CC that is preventing you from being effective in a fight. The tenacity bonus is very valuable, and you can always get more magic penetration later.

Situational Items

Abyssal Scepter: A strong item that brings both offense and defense. It is a wise pickup if the enemy is packing a decent amount of AP. If not, however, you should look elsewhere.

Rylai's Crystal Scepter: Good stats on this one, 100 ability power and 400 health. The slowing passive is nice, but not taken advantage of that strongly by Swain. Half of his skills already slow/stun, and it's only really useful with his ult, and if you are hitting them with your ult, you are already up close and personal, where slowing them down isn't that essential. Still, an ok item for Swain.

Liandry's Torment: If you decided to pick up Rylai's, this is a natural partner item to it. It brings more ability power, health, magic penetratoin, and a damage over time passive that is amplified when the enemy is slow. I don't often buy this on Swain, and when I do it's usually the last item. However, it isn't a bad item by any means. Get it if you like it, but only after your core items.

Spirit Visage: This is a really great choice for Swain, and could be considered a core item. The only reason I left it off the core list is because it is less useful if the enemy team does not have a lot of magic damage. This item gives great health and magic resist, 10% cooldown reduction, and a very nice passive that amplifies all of your healing effects, which means all those little birds that are out stealing health while your ult is active will be bring home 20% more health for you. Pick this up often.

Rabadon's Deathcap: I consider this a luxury item for Swain. No item brings a higher amount of ability power, which is a huge deal for a lot of AP mids, but Swain benefits from lots of different stats, not just ability power. Still, it's hard to deny the damage this item will bring you. If you are way ahead of your opponents, feel free to pick this up and watch them melt before you. I wouldn't buy it if you're behind though. You won't survive in a fight long enough for it to be effective.

Void Staff: This is how you continue to beat the enemy if they stack magic resistance. Check out what items your enemies are buying: If more than one of them is buying magic resistance, it's time to think about picking up a void staff. You will completely ignore 35% of the enemy's resistance, letting your damage remain relevant throughout the game.

Q: Decrepify
Swain's Q, when used on an enemy, places a bird at the point where you were standing. This bird begins hitting the enemy with a beam that deals small damage and slows them while they remain near the bird. If the enemy walks away, the damage and slow will cease, but if they come towards Swain and the bird, the skill will continue to affect them. It is useful for setting up your other moves, as well as slowing down an enemy that is advancing, allowing you to escape. This skill gets maxed last.

W: Nevermove
This is a fantastic ability. Swain highlights a circle on the ground, where, after a brief delay, any foe inside will be grabbed by claws from the ground for huge damage, and they will be rooted in place for 2 seconds. This gives you time to move in close to hit with your other skills. The length of this snare is huge; 2 seconds is a long time in this game, and the fact that it can grab multiple people is even better. I alternate leveling up this and E at the same time.

E: Torment
E is an interesting skill. Torment affects a targetted enemy champion, dealing a good amount of damage over 4 seconds. During that 4 second period of time, all of Swain's other attacks will also deal increased damage to the target. This means it's a great idea to lead with this skill, and then combo all your others to achieve maximum damage. As far as I'm aware, this is the only skill in the game that actually amplifies the damage achieved through the summoner spell Ignite, which makes it a great choice on Swain. Again, I switch off leveling this and his W.

R: Ravenous Flock
Swain's ultimate is his calling card. He transforms into a large bird, and continuously sends out three smaller birds that steal health from enemies around Swain. This move is great, and can remain active indefinitely, as long as you have the mana for it, but the longer it is on, the higher the mana cost is to sustain it each second. Turn this on in every teamfight to both deal good damage and keep yourself alive longer.