Swain can deal MASSIVE damage if you know how to play him right and almost NEVER DIE because of his ult
Swain can carry games HARD He shines mid game after he gets some items built and can get his team very fed if he is good
Early game you want to stay back and farm try to let the minions push to your tower so your jungler can gank and you can score some easy kills and money
You want to try to bully the other champion a little but play passive so your jungle can gank and you can get the kill
Your E makes your abilitys do 20% more damage to the person it is on so USE IT FIRST
With blue you are unstopable

To max your damage output first use your E then you try to land your W after that use your Q So it can get the max damage off and they cant run away if you have your ult try to stand close to them so you can do more damage faster unless you are getting focused or you are low HP

Your Q Doesnt have a cast time and you dont have to turn around to use it so its AMAZING to get away with while you are running

If you get tower dived make sure your ult is up and Q the person chasing you and W them right after so they wont be able to get out of your W cause of the slow from your Q. For a last resort right before you die try to get your W off on them if you do you might be able to get a kill

I dont like getting spell vamp because you dont get that much spell vamp from area of affect (AoE) Witch that is what swain is

I personally like to bum rush their team if i know my team will follow up and try to get my W on as many people as i can. Make sure your ult is up then E Q W Their ADC or APC then use hourglass in the middle of them when you get around half HP only if you are ahead in gold and you think you can win the fight