This guide is still a WIP, but the basics are laid out. I will go more into strategy and such in an upcoming update.
Hello everyone, my name is Eddy and I am here to show you how powerful Sion can be. Sion is often on the lower parts of tier lists, so many people overlook him. But he is a very dangerous foe if played correctly - many build him as an AP caster or stock him up with health items and try to tank with him. But in my opinion the most effective manner in which Sion is built is perhaps the most obvious one: pure unadulterated melee DPS, baby.
Sion at first glance is a champion that seems to be a one-trick pony: a two-second stun (Cryptic Gaze), and not much else. I'm not going to sugar-coat the facts here: your first glance is mostly correct.
Cryptic Gaze: People watch for the stun, both allies and enemies; you are simultaneously at your most dangerous and most vulnerable point after you use it. So get good at it! Know when to deploy it - with my build, your mana pool will be at a minimum, and thusly your ability to spam Cryptic Gaze is a commodity not to be wasted. Runes help with your mana pool initially, and careful usage of the skills available to you will ensure that you're not particularly mana-starved. Mana potions also do the trick. Take this move FIRST if you plan on getting first blood; otherwise choose Enrage.
Death's Caress: Almost worthless for an AD Sion. You may grab it at level 7 or 8 if you are getting focused down every team fight, but generally choosing to max out Enrage and Cryptic Gaze before even touching this skill is the usual route - all it does is waste your precious mana!
Enrage: The sweet taste of victory. The health cost is negligible, even at low levels. The damage boost is insane, pure and simple. This is what makes AD Sion so wonderful: keep it on at all times and max it out whenever you can, ulti excluded of course. You'll be hitting much harder than they expect and that's what makes you particularly dangerous. Also with this skill, your health is boosted decently by the time end-game rolls around.
Cannibalism: A solid ultimate. A fairly low cooldown (with The Brutalizer) ensures it'll be up for most team fights, which is the only time you really need to be popping it. Pop it 1v1 as well, but in a gank it's unnecessary unless you are going hard for the kill and want that sick IAS or the lifesteal for a bit of tower diving.
What AD Sion Can and Cannot Do.
-Tear apart most non-tanks in the game
-Jungle decently if you decide to buy Vamp Scept a little early
-Chase down heroes with BoS + Ghost (if you choose it) + Stun
-Do steady damage: just point and click
-Soft initiate with stun (Much easier on TT)
-Farm easily with Enrage
-Take on 1v3s very well (prone to CCs and nukes)
-Tower dive well
-Escape easily without Stun/Ghost
-Hard initiate (run smack into 3 enemies, like Malphite)
Remember, you are a cannon. Not necessarily a glass one if your ultimate is up, but be wary of people trying to focus you down. This build is designed for maximum carnage, not necessarily concern for your life. Obviously, don't be overly aggressive, but remember that last hits are the foundation of your income and certainly necessary to succeed in the game in general.
I personally use either Cleanse/Exhaust or Ghost/Exhaust. Clarity and Ignite are both good alternatives if you dislike my preferred setup.
If you're stunned or blinded, you're probably dead, so I recommend keeping Cleanse handy, but Ghost can chase down those cowardly bastards with ease. Ghost is much better on TT, since it gives you good map control, and less effective on SR. In the end, it's up to your playstyle.
This is simply my preferred rune set-up. Pretty standard ArPen/Mp5 per level/flat CDR/flat HP.
Long Sword + 1 HPot when spawn
Boots + Upgrade to Brutalizer 2nd time back, possibly grab 1 MPot if desired
Upgrade to either Boots of Swiftness, Ninja Tabi, or Merc Treads
Buy Vamp Scepter + Buy Zeal
Upgrade Vamp to Stark's Fervor
And from here you have the option of either completing Ghostblade and Phantom Dancer, or going for Atma's and Phantom Dancer. Frozen Mallet is also a solid choice.
Most games with this build don't last past Brutalizer + Boots2 + Starks + Zeal
Long Sword + HP Pot
Boots + Brutalizer
Vamp Scepter + Boots 2
I've changed the items around from when I first made this guide - you will be much more of a help to your team w/ Stark's Fervor, especially in Twisted Treeline. Plus you will not be so squishy if you get either Atma's or go for Phantom Dancer. If the enemy team is mage-heavy, get Wit's End and/or Banshee's Veil. If melee-heavy, the basic loadout should do.
Play smart, but aggressive. Know when your enemies have overextended, and coordinate ganks. With his stun, Sion is a handy ganker from very early on. He is especially effective in TT, not as much so in SR.
Have Enrage up at all times. And last hit, for crying out loud.
Wait for your tank or whoever has the intestinal fortitude to initiate first in a team fight, then pop your ultimate and stun whoever is being focused down. In early/mid game you will likely have to use Exhaust right after to ensure a kill; in late game he is probably already dead. Remember that you should always be attacking when your ult is up! Without that lifesteal, you become rather squishy. But that doesn't mean that you have to overcommit to every fight - know when to run, and Exhaust/Ghost if necessary.
Early Game Specifics: You'll be somewhat squishy, but with Enrage on you can do some surprising damage, particularly on crits. Keep to a side-lane and gauge if you and your lane partner can score an early kill off a stun if they push near your tower. Other than that, be certain to last hit as much as possible. Enrage will make this process easier.
Mid Game Specifics: Once you get your ultimate, you officially have started rolling. Start ganking, and when teamfights occur make sure to contribute. You do a solid amount of single-target damage at this point even without Cannibalism active, so you can really burst someone down easily if they're caught off-guard or have no escape option.
With Brutalizer, Boots of Swiftness, Vamp Scepter, and Zeal, your core build is almost complete. Just keep farming, ganking, jungling etc - you want to be making as much money as possible during midgame. Do your thing, make some moves. Grab a Banshee's Veil if you find that they're packing some heat; get armor if the opposition is Xin Zhao, Panth, or hell, even another AD Sion.
Late Game Specifics: With Starks, you are a boon to your team. Don't initiate unless you know what you're getting into - you're excellent at sweeping up, or rushing in behind tank, but don't look at your massive health bar and start thinking that you can do some dumb stuff - well, you can, but KNOW YOUR LIMITS! And have fun.
More to come in future update!