With this build, you will be capable of dominating your lane and also carrying the team as a Swain. You will also find that you are unkillable due to the your incredible survivability. You will possess powers to jump into or initiate team fights with ease and also make it out alive. This build is a late game build so try not to stress if you are finding it difficult to get kills during the early game however, the rune and mastery setup will help you to dominate your lane.

You need these runes in order to penetrate your opponent's magic resist during the laning phase. This allows you to burst more damage therefore wearing him out and revealing more chances of kills.

Getting magic resist per level runes for swain will maximize his survivability during late games. Think of it this way, if an AD carry attacks you, you can easily regain the hp back from the ultimate. Whereas, if a super beefy AP carry (example Malzahar) hunts you, his damage output can be reduced with the magic resist per level runes.

These flat AP quintessence will allow you increase the damage output of you skills during early game phases. In a way, these are like the magic penetration marks listed above. During early phase game, if you are the carry, you try to dominate the lane so that the opponent will not be able to match your power during group fights.

For the offense masteries, take the AP per level, 15% magic penetration and ignite. These masteries will allow you to COMPLETELY dominate your lane. The AP mastery will also buff you up a bit if it scales into late game.

For the defence mastery, take the armor, magic resist, block physical damage, HP, and the attackspeed/ap buff. These masteries will allow you to stay durable in your lane. It is important that you do not recall all the time because over time your opponent will outlevel you in lane and this opens more opportunities of them killing you!