This sion is VERY tanky. Mid game onwards you will have over 3k HP with 130+ Armour & MR. Late game that goes up to 5k health onwards. With that much health you are virtually unkillable... as long as you don't do anything stupid. Your damage output will hit about 200 in mid game rising to borderline 300 late-game. With attack speeds of around 1.2 a sec you do some pretty nice amounts of damage. Especially when your ult turns that figure into 1.6 ish.

Pros:
-A good but slow(ish) farmer late game.
-VERY survivable. Even in a team fight while getting focussed.
-Flat 2sec stun... probably one of the best stuns in the game.
-You have a LOT of attack damage without needing to purchase more than 1 DMG item.
-You need your atmas, greaves & starks. But after that your not item dependent at all.
-Your ult lasts for ages and it even has a reasonable cooldown.
-Almost unbeatable in 3v3. If you play smart you can 1v3 them late game.
-Relatively easy to learn.

Cons
-Quite difficult to be very good in 5v5.
-Annoyingly squishy early game. (especially after that patch, thanks riot).
-Takes a while to get going.
-No escape ability. You have to rely on your shield and hope.
-No long range poke.

Armour pen marks help with damage output better than anything else you could want.

The HP/level seals are there because +175 health at lv18 is flipping fantastic for someone that gains dmg for having more HP.

Shield glyphs are to help against nukes before you get your FoN.

Fort quints are to give that much needed boost early game.

1st lv stun is for help with fb. If you end up with a solo lane or with a champ very bad at getting fb (eg ezrael) then go straight with enrage.

If you don't get it lv1 then lv2 is for stun. After that you should max out enrage as soon as possible, any extra lvs going into your shield as it scales better a lv than your stun does. Your ult gets maxed aswell of course whenever you can.

I go full defence because despite your masses of HP you don't tend to have that much armour and the extra DMG reduction it provides is really nice. The +4% attack speed bonus is good aswell as with greaves + starks + ult you get an extra 2.1% attack speed. It doesn't sound like much but honestly it does make a difference.

Ghost is absolutely neccassry for sion. It's his only way to escape. Flash is for more fragile champs, sion can take a hit or 2 on the run so ghost is prefered. The great thing about it is it helps you catch squishies as well, 1 hit from your hammer for the slow + ghost and they're as good as dead.

3v3

Grab your stun and a vamp sceptre and head for the lower bushes. Pick on the squishy and the second he turns to run hit him with your stun. If you have another stun on your team fb will be easy otherwise you'll have to time yours perfectly. DO NOT RUSH AFTER HIM, if your about to loose him set an ignite and go back. You cannot afford to give up a kill early game with sion. He has a bad enough start as it is.

Head up top (sion MUST solo top in 3v3, if you can't you should probably leave, no other champ is as good as he is top and he needs it), last hit minions as much as possible but don't try and harass. Back off and keep last hitting. Once you hit lv4 pop your shield and stun your target then go in for 2 attacks and leave, blow up your shield just as your about to leave it's range. Most champs will try to get a spell back at you so try to keep your shield up till the last sec possible. Do this again, do not go back until you have enough gold to upgrade to a belt & greaves (1270 gold). At lv6 do it again except this time hit him with your ignite and ghost into him. You should be able to kill any carry (which normally go top). If your against someone that healed before or is another tank then obviouslt don't go for it unless your sure you can get the kill. Remember, last hit as much as possible getting the health from enrage it VITAL for sion.

5v5

Much of the same as 3v3, the difference is that unless your with someone like jax or pantheon you should probably get enrage first. Co-ordinate your stun well and you should be able to get quite a few kills in if you make sure you hit it at just the right time. The best champs for sion to lane with are pantheon and fiddlesticks. Taric, jax and corki are also great.

Once you have your greaves and belt it's ganking time! Sion is an excellent ganker because of his stun. Unfortunately he can;t get to other lanes fast enough so you should call for support and try and get ganks in your lane going as much as possible.

Hopefully if you got a couple of kills in you should have a starks as you go into midgame. What you need to do now more than ever is farm up as many last hits as possible. Lane for as long as you can and don't leave unless absolutely necessary or there is a gank threat. This would be bad advice for most champs but you need to get those health stacks up. Try and get to 3k+ health as soon as possible. Go back once you can afford your atmas. Once you have your atmas you can really start to make a contribution that will blow your opponents away. You will hit about 200+ damage and 3k health at with your atmas at around lv11-13 depending on how much you killed. Your job is now simple.

Be the tankiest tank in team fights. Make sure you go in as one of the first and get as many hits in as possible with your ult active in order to soak up as much damage as possible. If you have a good team then as you absorb insane amounts of damage your opponent's should go down extremely fast as your team is almost free to do whatever they want. After the inititaly burst of damage goes off sion tends to look fragile with low health so any average player will keep hitting him while your ult will just let you take it. Use your shield whenever you can to soak up even more damage and stay in there.

When to use your stun: If your against opponents like fiddle then wait until he comes in and then hit him with it the second he tries to drain. He will go down like a shot. Do not initiate with it but wait until an opponent is trying to get out and then stun and ping them up.

Just remember to stay last hitting minions as much as possible even this late in the game. You need to farm up as much health as possible.

It's hammer time! Honestly. Your frozen mallet now lets you do your job to your fullest. When the team fight starts, choose a carry and ghost into them and then ping them up. Your slow will let your team run over them with ease. If they start to get away with flash etc then drop a stun on them and finish them. Then choose another target and keep going. Get in there, absorb loads of damage and batter your way through their carrys keeping them slowed for your team. Get those kills and they'll either surrender or you can get the gold for your FoN and wamrogs. Usually you wont finish much after your mallet as you'll probs win.

Always remember to last hit and farm whenever you can and get those health stacks up. Kill dragon when needed and keep stacking health. You will easily reach 4k health and 270+ damage. The amount of damage you do is actually quite a lot but what makes you is the fact that while your battering your way through your targets you gaining 120% of the damage you do as health. Against champs like vlad tha have high health but low armour, if you hit them all the way from full to 0 health that means your opponents will have yo go through all of his health AND all of yours to kill you. 7000+ health with 130 armour is not something that is going to die any time soon.

One champ to avoid is tryundamere, once he hits 0, life-steal no longer works and he WILL kill you. cc is sions only weakness as it stops your lifesteal. If your against a heavy CC team try not to go in first but wait until another tank has gone in before you initiate. With your ult active you are virtually invincible.

Core

Atmas's Impaler

A note on berserker greaves: I know that it's "nooby" to have them but sion needs them. The attack speed bonus he has is low due to buying other more important items like frozen mallet and atma's impaler. As a result he has to get the extra boost from somewhere. This is where.

My item build up to frozen mallet is described above. The last 2 items vary a lot, here is a run-down of the options:

The health regen means that at 4k health you get 14 health a second in regen... that is a LOT. The movement speed also helps to move those few extra feet to get your frost hammer in. The magic resist will also balance out with your armour.
Get: Against a team with 2+ casters in it.
Do not get: Against a DPS dominated team or against multiple ignites.

Wamrog's Armor: The masses of health will take you to easily over 5k health. I once got to 6k after I bought this item. No-one can handle 6k health without a lot of effort. Good for almost any situation. The 1450 health means +29 extra damage as well which is nothing to scoff at.
Get: If you find your self a little bit fragile and still die occasionally.
Do not get: If you never get focussed and very rarely die.

Puts you at 230 armour. Which is enough to put any DPS champ at bay. Also think, if you have 4k health then killing you will deal 1200 magic damage back... add in a life steal of around 2000 more and that means this will deal at least 1800 magic damage in total before you die. That is a scary amount for any kind of scary DPS champ.
Get: If your having trouble against a fed yi or fed ashe etc...
Do not get: If your against a lot of casters or you arn't getting focussed.

Puts you at around 175ish armour or with thornmail 275ish. If your having trouble against DPS champs normally go for thornmail first. Only needed if you keep getting focussed by teams containing champs like ashe, yi, nocturne and tryundamere.
Get: Against teams containing lots of DPS champs that tend to focuss you.
Do not get: Instead of thornmail.

: Maxed with your ult and fervor will give you 145% lifesteal and around borderline 400 damage. If your team is all very tanky get this to help deal that extra amount of damage. It also adds survivability in a lot of ways with even more lifesteal.
Get: If your team needs a damage boost.
Do not get: If you do not need any more damage or your getting focussed and will loose the stacks.

Combined with your ult and frost hammer you can PWN anyone. An absolute must if you got fed as it will allow you to keep on carrying and getting kills to propel your team forward to victory. It also works out with atmas and basic crit chance to around a 40% crit chance which is nice. The CDR is also fantastic to make sure you always have your ult ready and let you stun more often.
Get: If you got fed.
Do not get: If you didn't get fed.

The next are 2 rare item combinations I use and when/why I get them:

I get this VERY rarely and I use it if my team is having trouble finishing opponents off after team fights. You will actually very nearly hit the 100% crit chance with these 2, combined with your attack speed will allow you to do crazy amounts of damage. No champ will get away from this combined with your frost hammer.
Get: If your team is struggling to finish off targets after team fights.
Do not get: If you get focussed.

I get this if our team doesn't have a carry or your carry isn't fed and you are. Because someone has to step up to the job. If your reasonably fed than grabbing these 2 will allow you to do so much damage your opponent's will start s***ting them selves at the sight of you. It will only work if your fed enough and are already tough enough to very rarely die.
Get: If your fed and need a carry.
Do not Get: If the enemy team is fed enough to be able to kill you by focussing.

Well there you go, my first sion proper guide and one of the few AD sions guides out there. Not enough people play AD sion. In 3v3 this build will let you own so easily it's a joke. In 5v5 you won't be as strong but will still be a dominating presence.