Hello there! I am not very high up in tier, but I would still like to tell everyone of my build with Sion. As i write this build, I have an 80% win-rate with him while having a load of fun. I started in Silver 5 and did not play ranked for a while after that. But with old Sion he was quite a bit different and I enjoyed him also, but the rework was a gift. I started learning him and experimenting with his builds and played normals. I began winning games constantly and then took him to the ranked fields of justice. I quickly began winning, and I have now gotten to Silver 2 only playing 3 weeks worth of ranked. I can say he carries me on his big, broad shoulders. Hopefully you like this guide, it is my first and I would love some feedback!
*UPDATE* I just got to Silver 1 using this build, I am now 23-5 with him.
I will say that this guide is not meant to be an extremely tanky Sion as I prefer to use his damage, and build him only a little tanky. His Soul Furnace and one or two tank items are enough. Please consider that this is a guide for mainly AD Sion.Update
I just made it to Gold 5 mainly using Sion to win games. It has been a great success, having only a few more losses.

Pros
-Very Powerful
-Deals a ton of damage when landed
-Has the cc to combo with
-Longer the game gets, more hp
-Versatile
-Strong split pusher
-Can carry (land the ults and q's)
-Strong all game



Cons
-Easily kited
-Can be squishy
-If you can't land your combos or ult, you will be useless
-Easy to dodge
-Passive is useless when stunned

Sion's ganks are among the most unique. Coming in from the river almost never works, so being by the lane you are ganking is important to time it right. Once you hit 6, you should immediately think about where you can Unstoppable Onslaught and land a kill. Bot lane is usually the best spot, as you will probably hit at least one of them. Top is also a good place. Mid lane is harder with people such as Leblanc or Zed who can dodge your ult easily. When you ult want you to drag the cursor the the end of your screen and look at the edge of the screen and your minimap to make sure you are going the right way as you do not want to miss this. Most people will be surprised about the ult, even your allies, and will not always be prepared so make sure to tell them to be ready that you will gank at some point.


Landing the Unstoppable Onslaught is easier than some think (but I am in silver atm), you have to meet them where they are going, and try your best to predict their movement (this is why mid is the hardest to gank, but can be done). If you miss your ult, stop it immediately, there is no point in running past your enemy. But when you land it, charge up your Decimating Smash right after, at least until half way as you will not be able to get the full thing off. Also having your Soul Furnace on before you ult is more damage when you land it as you blow it up. The amount of stuns you get from it will last a long time. But your laners will still have to help if they are at full health. You can also dive under their turret with your ult if you are at full health and your team follows up, as it will chunk the enemy, stun them, and you will have time to escape.


If you must come in from river, hope that they come near the bush, but if they do not, turn on your Soul Furnace, make sure to hit them with your Roar of the Slayer, and have your laner follow up so you can land you Decimating Smash. This is more than likely secure the kill. Coming in from the tri-bush top lane is also good to do, and can burn a lot of flashes.

Glory in Death
This is your passive that will deal a ton of damage. It gives you lifesteal that you have to use in order to stay alive in the passive, but increases your damage. You can speed up yourself in this by pressing any ability key, but you will decay faster. The 50% movement speed buff helps you catch up to your opponents, but you can still be kited. Always go for whoever will not escape you, or does not have flash up. You can use the Ravenous Hydra active also once you have given yourself the movement speed buff. Sometimes it is ok to die in order to use your passive, but not always. You will supply no cc and can be worthless by just being stunned or snared. You can also use this to finish off a camp if you will die because you do not lose your buffs and will respawn right after.

Decimating Smash
This is your main skill, master the timing of it and you will do great. It supplies you with a slow and stun, while also dealing a ton of damage if you can fully charge it. It decimates (heh) the enemy team in teamfights when you charge it halfway or full and get the stun and damage off. It can completely turn the tide of the battle.

You want to start with this at level 1 instead of the shield as it will increase your clear time. The 10 hp you get from the first camp will quickly be made back since you can clear faster, and help more lanes. Just pressing on the on QWER (any) will slow the enemy and do a little damage, but charge it halfway, it stuns the enemy and does more damage, then fully charging it stuns them for a long time and does even more damage!! Always use this after your Unstoppable Onslaught and fully charge it before every jungle camp. When in a bush that is not warded, the enemy will not see you charging it therefore you should be able to get a fully charged strike if you time it well.

Soul Furnace
This ability decides what Sion is. The old shield of death did not fully disappear (thanks Riot) and is more helpful than before. For every small minion you kill, you permanently gain 2 health, and for every large minion, you get 10. This is why I think he belongs in the Jungle, as he can abuse this passive much more. But the shield also uses 10% of your max hp and 40% of your Ability Power. When clearing camps, turn it on but blow it up right before it dies out for more damage. It also will do quite a bit of damage mid-late game. This also deals % of their maximum health so it is great against tanky targets.

Roar of the Slayer
I used to max this second, but I find it does not do as much as one would want. But, it supplies a slow that improves as you level it. Using this, you can hit any minion and launch it hitting your enemy and slowing them, reducing armor, and a bit of damage. It is also very good to do when clearing camps before mid game as it stuns minions when they hit a wall. You can use this to hit Malzahar's Voidling too, or Elise's spiders. This can be used in teamfights to reduce all of their armor and slow them.

Unstoppable Onslaught
By far my favorite ability in the game, landing this gives you satisfaction like no other. It is possible to get triple kills with this just by landing it. But it allows you do run without getting cc'd and slam into an opponent and stun them. At first, this has a very high cooldown so blue buff is good to have. But at higher levels, if you have cooldown reduction items, it will be up every 50 seconds or around there which is nice. This ult is easy to land if you play it right, know who does not have their flash up, as they are sitting ducks, but make sure to know who can dodge it like Graves or Fizz. The longer you run with this, the more damage it will do and the longer the stun it gives. Missing this could cause you to lose the fight and game. If your enemy is standing directly behind their tower and you will not be able to curve around, you can still hit them. If you slam straight into the tower while they stand next to it, it will still cause them to take the full effects and then they shall be slain by you or your team. The best thing you can do is run from your inhibitor to their inhibitor and kill them, it is the best feeling. The sound of the ult will also scare the enemies, as they will not always know where you are coming from as the river is useless, you just come from the lane that needs to be dealt with. Do not be afraid to use this at point blank to stun your opponent. It can also be used to scape.

Against 1 Enemy
Sion can usually win a fight if the enemy is not a tank or a Tryndamere. If they are melee, you have a much better chance, ranged you can get kited, but as long as you land your cc, you can win the fight. Make sure you hit your Decimating Smash and if you can get it halfway charged. Using your Unstoppable Onslaught at point blank is not a bad idea if it wins you the fight. You have enough crowd control to take control of the fight and enough damage to win it. But you also have to remember to use your Ravenous Hydra whenever you can.

Fighting Against 2 Enemies
You can sometimes win these, but you must kill either the squishy, or the damage dealer, as you do not want to die when you can get kills. You want to use your abilities, but do not forget, your passive is still there, make sure you do not die far away from the enemy so you can turn it around and get them. They will sometimes forget you have it too. On occasion, you might as well, but doing that will land you a kill.

Teamfights
Teamfights are where Sion shines. If all five are mid on the enemy team and you have four holding them off. Ping that you are coming and ult in, the enemy team will probably realized this and it will become chaotic. Try to hit their adc, mid-laner, or anyone that is easily killable. Charge your Decimating Smash and hit as many enemies as you can, and you can also burn many flashes doing it. Using your Roar of the Slayer on minions into the enemy team will slow them and reduce their armor by 20% helping your AD teammates do more damage. And your shield will either protect you, or do damage, or do both if you can time it correctly. With the Ravenous Hydra, sion becomes pure aoe and you will wreck in teamfights, even can win in 3v5 or 4v5 because of you.

In General
You have things that you have to remember, actives and timing. Being able to time your abilities is what makes you useful in the game, so if you cannot time them, do not play Sion. Your smite is also important to use in a fight if minions or something you can smite is there. It restores 15% of your missing health and mana, and can turn the fight in your favor. Most people will not know when you smite is up and do not know that you will get health back from it anyways.

Where I am so far in Silver 2, Sion is a great first pick. There are not any specific counters to him, Rammus could show problems, but then you just focus on other people they pick. Warwick is not a problem and he is a very popular pick today. You can cancel his ult with both your Decimating Smash and Unstoppable Onslaught. Always make sure you pick him when you can, and place your wards, as you do not want to be counter jungled (you need the cs). You should invade often in ranked, with Sion it is very easy as I said above.

Well this concludes my first guide, and on the champion Sion. I will be adding on to this guide with more, and I would love some feedback on what you all think! Making this was fun and Sion is by far my favorite champion. I hope this guide encourages you to play him and succeed!