Hi, I'm Rsquared and welcome to my Swain guide. In this guide I will describe what I believe to be an effective way to AP Offtank with Swain.

Benefits



+One of the best substance in the game.
+Built-in hard CC.
+Fantastic damage dealer.
+Great farmer.
+Lots of AoE.
+Can Tank in big team fights.
+Build in Will of the ancients.
+He's a big fupping BIRD!
_____

Drawbacks



-High mana cost
-Weak early game.
-Practise.
-Needs high mobility.

Greater Mark of Magic Penetration:Magic pen is a big deal on casters. These marks will help you punch through your opponent's base magic resistance, and with the help of Sorcerer's Shoes, allow your spells to do almost true damage to anyone without any magic resist. There really are no alternative marks.

Greater Seal of Scaling Mana Regeneration:you'll be mostly passive-farming thanks too these runes, so your mana regen from Doran's Ring, Meditation and Equilibrium should be able to sustain you enough to last-hit constantly. And even late game when blue buff isn't always available

Glyph of Ability Power: Thanks too these you will have a lot more AP then other mages mid that don't have these, so you can get really strong and out level the enemy.

Greater Quintessence of Ability Power:even more AP ^.

1. Greater Seal of Replenishment:If you have problems begin game with your mana then these runes are better for you.
   
2. Greater Seal of Scaling Ability Power:If you want more AP and runes to give you a stronger late game, these seals work pretty nicely.
   
3. Greater Seal of Vitality:If you're fine without mp5 runes, these seals will give you a little more survivability against mid game nukes and late game focus.
   
4. Greater Glyph of Scaling Ability Power:If you're very confident in a safe early game, these glyphs will allow you to snowball very quickly and get a lot of burst fast for stronger harass and earlier kills.
   
5. Greater Glyph of Cooldown Reduction: I usually don't take this one because of Deathfire Grasp, Sorcery, Elixir of Brilliance and blue buff, but if you want more CDR maybe to hit every minion with you Q, then this is a good place to pick it .
   
6. Greater Quintessence of Movement Speed: combined with Swiftness and Boots will give you a lot of early game mobility for dodging harass and getting in range for your stun.