Hello, this is the first build I've written for MOBAfire, after using this site for a while, I wanted to try my hand at it, so here it is.

Pros:
Great Damage Output
Incredible Survivability with Ultimate on.
If played correctly can take on more than one Champion alone.
Cons:
Things can get messy if you're caught without your ultimate.
Need to pay attention to your mana with ultimate on, don't let it get too expensive.
Only escape mechanism is Nevermove, try to hit it perfect if you're running away!

Flash, a good mobility spell, use it to get away from a fight or to chase down an enemy.
Ignite, a great spell for Swain, works amazingly with all of his DoT's.

OPTIONAL SPELLS
A good defensive, or if used correctly, offensive spell, use it to defend a turret from getting destroyed or teleport to a ward to get a gank in.
A replacement for Flash if you don't like it. Use it the same ways, run away or chase someone down.

9/0/21, excellent masteries for Swain, he doesn't need all the offensive ability of a full offensive mastery build, so I put the points in Utility for the extra survivability and cooldown reduction, the extra mana regen helps quite a bit as well.

This rune build is just a usual nothing special rune build, AP and Magic Pen, some people feel that Swain needs just a little extra mana regen, which is why I also put up the Clarity seals, but honestly, you won't need them, straight up AP is the better choice.

There you have it, i'll be adding results from games a little later on after I get a few more in, this is just a basic quick-reference guide for a decent Swain build, I hope you enjoy it and please try it before you vote at all, thanks!