This is my first guide, and (I think) a unique build for Swain. I usually find that this build works even if Im not being fed purely because of how simple it is to obtain most of these items. Swain is one of the most unique champions that Ive found in League of Legends, and one that is highly underestimated. Props to my cohort in the finding of this build, Sasashima.

Pros:

Will run out of mana less often
Can do amazing damage
Has stuns and slows
Can regenerate HP
After

Frozen Heart he can tank 2 or 3 champs at once and live


Cons:

VERY squishy early game
Must master

Nevermore placement for maximum damage output
Lack of Rod of Ages may make sub-par HP
Slow movement speed, even with boots
Can be easily KSed (Kill stolen) because of his damage over time (But hey, better the team get that kill then not get it)

Now onto items. I know this seems like a random assortment of items, but I assure you, it all works well with Swain.
-I always start off with boots to make up for Swain's lack of movement speed. They help a lot in the beginning. You can choose to buy pots if you'd like, but I dont.
-Open up with the Archangel's Staff because of its passive; 3% of your mana becomes AP-This build focuses around that single item.
-Secondly get the Tear of the Godess to add even more mana to your mana pool. Remember, the more mana you have, the more AP you'll have later.
-Finally I finish off my boots, of course for maximum damage output I choose Sorcerer's Shoes, but its really your choice here based on team composition and need.
-As the core part of most caster builds I, of course, have to get a Rabadon's Deathcap for that extra 30%. This item will boost your AP up to 250-300 depending on how much mana you've made with your Archangel's Staff and Tear of the Godess.
- Frozen Heart for its mana and defense. If you're against a mostly physical team this item will add survivability as well as mana. I love this item for the defense it provides for weak casters. But in addition it will give swain some extra AP to tap into also.
-And lastly, you could use any item you'd like here, I prever a Void Staff for the magic penetration, but any item adding mana or AP would also do well here.

I've yet to see a build for Swain that focuses on his mana hungry ult, and I think this one satisfies it as well as adds some massive damage output. Swain's ult will be able to run even longer now thanks to the extra mana in his mana pool. As well as the extra ult length, you'll get some extra survivability for those pesky champs like Tristana or Ashe. All around I think this build is a great way to counter Swain's mana hungriness.

Swain's skills all work very well together if you know how to use them. One thing Id advise for new Swain players is to master Nevermore. Nevermore is my favorite skill of Swain's, and it sets up for everything else. My normal combo before level six is to use Torment (E) and then Decrepify (Q). Torment allows more damage for Decrepify, and Decrepify will slow in order to
A)Finish off the enemy with auto attacks
-Or-
B)Land a Nevermore in front of him
So that would be E>Q>W, or if you can't land a Nevermore after Torment and Decrepify, W>E>Q.


After level six is where Swain becomes even more deadly.
The same combo applies, except anytime after you cast Torment, feel free to light up your ult. Your ult, like Nevermore, also has many uses. It can be used to heal HP, as a last hitter, or as a way to keep yourself alive in team fights, or while enemy champs chase you.

Usually after an enemy hits 1/2 health from Torment/Decrepify harassing, I find them an easy kill. You can Torment > Decrepify > Nevermore > Ult > Igniteand it will more often than not, finish the enemy. However you can also do Nevermore > Torment > Decrepify > Ult > Ignite and chase them down. If your enemy is not dead, but has low HP, chase them with your ult. Flash to them, chase them, stun them, anything you can to get that kill, but also watch your back for enemy ganks, or other team mates helping them in the lane.

If you think you can get the kill, ALWAYS IGNITE AFTER TORMENT. It will add damage. All of Swains attacks are amplified by Torment, and I cannot stress this enough.

All in all I think this build satisfies many conditions such as armor, mana, and AP. So give it a try and see what you think. It works for me, and maybe it'll work for you. But if all else fails, "Let's just morph and eat 'em!"