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.
DISCLAIMER: This build is 99% this build and about 1% my own opinion. I decided to post this build here on mobafire because very few of the Swain guides I've found build him the way I do, which I feel is the most effective method.
The key to playing Pain Train Swain is simple: Swain is a Tank. An AP tank, but a tank nonetheless. Building Swain accordingly will allow you to steam roll teams in a never-ending, unstoppable onslaught of power.
(Also, sorry to anyone else who thought of this name before I did.)