Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
There is alot of under rated champions in the game, But swain by far takes the cake.
I feel swain is one of the better harassers in game, He can also hold mid Lane very well.
Your BUILD with swain...
GRAB A RUBY CRYASTAL FIRST
If you are laning; try to play in the bushes as much as possible,
Harassment is going to be a big part with swain. unless they both come at you make sure to throw lazer bird on the enemy if they dont start playing the tower game. it will cost damage and will slow the enemy so they really cant get near ya. Also make sure to last hit the minions your passive gives you more mana regen back so more harassment when you kill the minions.
ONCE YOU HAVE 850g PICK UP A CATALYST
The catalyst is going to give you more mana, and also the oppertunity to lane longer.
If your last hitting the minions correctly you should have no issue gaining this much gold. (make sure to communicate with your laning partner so he also last hits: If you dont know what last hitting is, Last hitting is harassing the enemy champs as much as possible while letting the minions do the work on the enemy minions and you get the kill shot on them. it allows the minions to stay centered and not push to there tower so you can harass alot easier.)
NEXT YOU WANT TO PICK UP A BLASTING WAND
Blasting wand is going to give you a boost on ap, This is the point were you really start to notice how much damage your going to start doing to the squishies.
NOW YOU SHOULDN'T BE THAT FAR AWAY FROM ROA SO PICK THAT UP ASAP
NEXT YOU WANT TO PICK UP BOOTS
I prefer merc treds as swain you will be extremly squishy, the CC (crowd control) will rape you pretty hardcore.
TEAR OF THE GODDESS
One thing you will notice is when you use swains ravenous flock your mana is drained quite fast, when you pick up tear of the goddes make sure to spam spells as much as possible so you can get better mana and mana regen.
REMEMBER THAT TIME WERE YOU THOUGHT SWAIN WAS EXTREMLY SQUISHY? WITHA GOOD AMOUNT OF AP AND HIS ULTI IT WILL be alot more complicated TO TAKE YOU DOWN. I consider whis item as one of the most important items in the build for that reason alone.
PICK UP ANOTHER BLASTING WAND
Not only is roa giving you ap but now you have another big chunk of ap to drill you opponents with.
All that hard work you did building up that mana with the spamming of the spells has finally paid off. You are now getting ability power based off of a percentage of your mana, and you have great survivability. YAY.
Zhonyas rigng i feel is one of the best items in the game, If you are being focused. YOU WILL BE pop zhonyas with your ulti up and it will continue to heal you throught the duration of zhonyas. Zhonyas is another Very Important item to pick up on swain.
The last item is all based on game play...
I normally switch between these items...
Void staff - Gives you the proper magic penetration for the non squishys.
Rylai's Crystal scepter- allows you spells to slow the target for even more.
Banshees vail - allows you to block one spell every thirty seconds, And gives you more mand which thus gives you more ap also.
Make sure to only use ignite when your torment is on them, that combo alone can drop and enemies life pretty far. Expecially early game. Once again make sure to harass early game and last hit minions as much as possible. very vital for Swain. and be safe with your port dont waste it right away, I use my port to port in to group fights, I cant count the amount of times i have had double kills or triple kills because of my teleport. And last but not least. Make sure that you wait to jump into team fights, You may be harder to kill; But if someone throws an ignite on you that takes away alot of your healing.
The reason i don't describe what to do early game mid game and late game is because everybody is different in there play style. So i dont want to tell someone how to play just what to pick up.