Sion mid? Yes. Let me explain why.
1. W can block any pokes
2. The threat of Q and W combo can intimidate enemies to keep them out of exp range
3. Q and W combo does huge damage early on with Mpen runes, potency quints, and force seals.
4. Farming enrage mid will give you a huge health advantage, and with Atma's Impaler a huge dmg boost by late game.
This build starts AP and adds heavy AD towards the end. The theory is that in early game to mid game your Q W combo will DESTROY anyone, as AP sion always does early game, but the AD items that you grab later in the game let you still be useful in the late game battles and let you utilize your awesome ultimate.
Disagree with something? Suggestions? Let me know, I'll do everything I can to improve the guide.
1. 2 second targeted stun.
2. Poke-blocking, hero-popping shield
3. Ultimate that lets him heal entire team or even 1v2 or 1v3
4. Pretty tanky
5. FAST (this build)
1. Has to get close to dish out damage
2. Banshee's veil destroys his combo and chasing potential
I build the runes towards AP to give his spells the power they need to destroy early and mid game. This typically lets you outfarm anyone mid - Even a Kennen, Karthus, Sivir, or Kat, and rack up early game kills with ease.
Greater Mark of Magic Penetration for Mpen.
Greater Seal of Scaling Mana Regeneration to let you spam you spells. It is almost equivalent to the flat runes at lvl 4 (4 mp5 vs 4.1 mp5), which you will reach quickly, so its better.
Greater Glyph of Scaling Ability Power for that early game power - Yes, it takes until level 5 or so to catch up to the flat Greater Glyph of Ability Power , but mid this isn't an issue.
Greater Quintessence of Ability Power: unlike glyphs, it takes about 12 levels for the Greater Quintessence of Scaling Ability Power to catch up to the flat bonus. The 15 AP early game means 30 more damage from each Q W combo.
Greater Quintessence of Desolation could make a lot of sense instead for late game, but I enjoy early game Sion's power so much that I can't bear to take away from it. Its your choice.
Two things are absolutely crucial for early game: the Mpen in offense and the mana/lvl in utility.
The rest of the points go into AD bonuses in offense for late game. Theoretically these points could go into defense, but unless you play incredibly stupidly you shouldn't need it.
W is the most important spell on mid Sion. It can be both a strong defense and a great offense. I level it first because it needs to be kept up with the strength of your opponent's pokes. Also, W does more damage than Q, so you only need one rank of Q to stun so you can pop your shield on the opponent.
Q's biggest use as mid Sion is the stun, which doesn't change with lvls.
E is incorporated somewhat because the farmed health is nice.
R of course take whenever possible.
Start with a Doran's Shield and a Health Potion. This, combined with your W, will make you able to handle anything anyone can throw at you mid and let you stay there as long as you like.
Next, pick up Boots of Speed and Amplifying Tome. If I can't afford Sheen as well at this point, I like to grab an Elixir of Brilliance. The added AP and CDR will be enough to let you keep the enemy mid out of EXP range or continually force them back, and is well worth it.
Now start working on your Trinity Force and your Mercury's Treads based on the opponent you are fighting mid and how the game is going. If you're up against someone like Malzahar or any AP champ, finish Mercury's Treads first.
NEVER GET Berkzerker's Greaves.
NOTE: Guardian Angel (or Banshee's Veil) can be put in at any point after this. If you find yourself too weak, which is unlikely, grab it. I typically don't need it until my last slot opens.
Next, get Atma's Impaler. This will suddenly make your autoattack devastating.
I also like to grab Vampiric Scepter at this point, even though The Bloodthirster is still a ways away. The lifesteal can be a godsend and let you stay out longer without having to waste your ulti on creeps to heal.
Next is Phantom Dancer. The MS is great, the AS is great with your huge AD, and the Crit chance brings you up to 70%. Nobody will ever escape, and your ulti should take you from nearly no health to almost full health in the time it takes for the enemies to pop your shield.
The Bloodthirster rocks on Sion. Combined with his ulti, you should be able to regain almost all of your health in a very short amount of time. You can lifesteal tank for your team at this point, and potentially have better luck than your main tank. The additional AD makes him even more devastating.
This build seems to work well for a much larger variety of enemy team compositions than most. There are still, as always, some other choices for items:
The CC reduction and MR from Mercury's Treads are wonderful and make your ultimate more potent, but if the other team is low on CC and magic damage the Mpen from Sorcerer's Shoes is a better use of your money. This is an extremely rare swap to make.
Grab this item if the enemy team has too many stuns. As long as you are attacking and your ulti is active, it is very unlikely that you will die, but if you are stunned then the enemy team can burst you down.
Grab this item if the enemy team gets a decent amount of armor.
Grab this item if the enemy team has a moderate amount of armor, but not huge amounts. If 2 of the enemy team has 70+ armor but the rest have <60, this is a better use of your money than Last Whisper. Plus, more crit chance, and AD is always fun, and the move speed buff will put you over 500 when active to give you even more control over what goes on in fights.
Strategies for mid Sion
One of the best parts of mid Sion is the psychological warfare that can go on. Here's some tips:
1. Make them afraid of you.
If they are overconfident, stun them and pop your shield on them. This should take out a healthy portion of their life.
By doing this, they will learn to stay away from you when your shield is up. After they have been damaged by your combo once or twice, turn on your shield and leave it on, then chase them away from creeps and attack theirs from behind. They'll be out of exp range, and if they come close enough, stun them and pop your shield on them.
2. DON'T PUSH WITH YOUR SHIELD.
It's very tempting to pop your shield on the enemy minions to damage them. If you do this too often, however, you'll push too hard, causing you to overextend and, more importantly, making Tip # 1 impossible to utilize because the enemy champion is too close to their tower. Get used to the range of your shield and use it to last hit a minion or two without damaging the others (unless your opponent is pushing hard) if the enemy champ is out of range.
3. Save your shield for the pokes.
Don't use your shield constantly. Wait for an opponent to try to poke you, then block it with your shield. Your opponent should do very little damage to you overall.
You can also use this to force your opponent to drain their mana and waste their abilities. Charge at the opponent seemingly recklessly, and when they turn around to hit you with something, use your shield and stop chasing. Obviously, this only works with mana-based champions.
4. When you're low, bait them to you.
With your early game AP, you're shield will add a ton of durability to you. Pretend to be overconfident, and when your opponent charges at you, use your shield, stun, ulti if you have it, and hit them. If they stick around, pop your shield for the finishing blow. It takes time to get used to what you can and can't get away with, but its almost always more than your opponent expects.
5. Here's some obvious, stupid, and general ones that I see too many people screw up on:
i. Leave your E on.
ii. Last hit only - and emphasize it. Last hitting is your key to victory.
iii. Don't spam your stun without your shield ready to pop. Save it and your mana for when you need it.
iv. Have fun! Everyone screws this one up and gets too serious. >.<
Peace guys, and enjoy!