This build is all about blowing people up with your shield along with getting an insanely strong shield putting a certain ***** robot to shame.

Mark of Insight is a bread and butter Mark for any AP build that actually wants to do damage so not much explaining is needed here.

Seal of Clarity was chosen because Sion likes to eat up his mana so these are necessary for any AP Sion who doesn't want to recall after 30 secs or spend all his money on mana pots.

Glyph of Force was chosen because everybody loves to do more damage! The scaling on these runes allows you to just keep getting stronger without having to worry too much about early game because of your items.

Quintessence of Force for more AP! WOOT!

A pretty standard Mastery for an AP build but focusing more on anything to make my mana actually be there when i need it.

Flash is extremely good at using to escape from any sticky situation along with being great for catching those pesky running things. It is incredibly good for using to leap over minions at people with and detonate your shield for half their health.

Sion lacks the ability to chase people after his stun so he needs this dot to finish off those pesky runners again.

Clarity is also a good choice for Sion because he runs out of mana FAST! However i tend not to choose it because i can get enough mana regen from my runes and ring to last until i get my Meki's Pendant and book.

A big part of Sion's skill sequence is knowing when to put his shield up, with practice you can time it so the moment you arrive at the enemy your shield is ready to go BOOM! You will want to open the battle with your Deathfire Grasp taking off a third of their health, after this you want to pop your stun, run up to them and detonate your shield. If they are not dead after this then just wack em in the face a few times until the last of their health is gone.

Sion is amazing at Farming, just detonate your shield in the middle of the creep wave and they are all dead. Its as easy as that.