This is an Introduction.
When Orianna first came out, I was mesmerized by her unique and interesting play-style. When I purchased her and used her, I realized she was too circumstantial to be an AP Carry or Mage. Her spells are extremely predictable when she uses them for offense, and her scaling isn't too great anyway.
I am not saying that anyone who plays Orianna as an AP Mage is bad, but it's like playing Zilean the same way. It can work, but they're both way better off as supports. So without further ado, here is my guide to building a support Orianna.
PS: This is my first guide. Constructive criticism, please?
I take Armor Runes on Orianna simply because at level one, she's just about the squishiest champion in the game with a jaw-dropping base armor of 8. Although she has pretty good range on her spells, Orianna needs to stay within range of her laning partner to be effective (until level 2) and leaves herself very vulnerable to attacks.
Although Orianna's spells don't take up an overwhelming amount of mana, you will be using spells often. Mana Regen is ideal on her for early-mid game sustainability. By the time late game rolls around, you have enough Mana to not be running too low thanks to your Archangel's Staff.
I take AP per level runes instead of flat AP Runes because the latter will only help me once in the game. AP Per Level grants me a nice little boost of AP on top of what items I have. I will admit, it is very nice to have early game dominance with flat AP Runes, but Orianna isn't too much about damage, but a different kind of support...
What little damage Orianna will be able to deal over the course of the game will be amplified just a little by the Magic Pen runes. They stack nicely with the Abyssal Scepter, so it is very worth it mid-game.
Just your standard support masteries. Nothing special there.
Ah, yes. Items are what will make or break the game for Orianna.
I start with a Faerie Pendant, 3 Health Potions, 2 Mana Potions, and a Sight Ward, even if there is no jungler on the other team.
On my first trip back, I normally have enough money to buy either a Philosopher's Stone or a Mana Manipulator, and basic boots. Depending on my lane partner, I pick between the first two items. If you are laning with a mana-hungry champion or if you find yourself running low on mana a lot, take the Mana Manipulator. If your partner is getting very good CS and you don't need to spend too much mana on them, get yourself a Philosopher's Stone to increase your gold income without having to farm yourself. Orianna is a little expensive to build for, so this will come in handy later.
Grab wards, you'll be needing them, even with your Q and CV.
By the second trip back, I like to build my Ionian Boots of Lucidity simply because Cooldowns are a big problem on Orianna for most of the game. From there, I start building, if not straight out buy the Tear of the Goddess. Orianna will be constantly casting spells all the time, so this will be very helpful to her late-game. If I still have money left over, I build a little towards the Soul Shroud.
Again, take wards.
By now, you should have completed your Archangel's Staff and Soul Shroud and have started working towards the Abyssal Scepter. Both of these items will help turn team fights in your favor, specially with Orianna's handy R to really make a difference. Build the Reverie if you are loosing team fights and need to escape faster. When combined with your W, your team's movement speed will skyrocket.
If the game is not over at this point, the Abyssal Scepter is a must. If you are against a very AD-Heavy team, a Frozen Heart will provide a nice armor, CDR, and MR boost. If you are getting focused, consider a Zhonya's Hourglass to discourage focusing or to switch the attack over to someone else while you plan an escape.
OTHER ITEM POSSIBILITIES
Rod of Ages: This is an alright item and I really like it. If you find yourself craving extra HP and a little more AP and Mana, by all means feel free to take the Rod. Just remember that this reduces your support capabilities.
Ryali's Scepter: Extra HP is always nice, and slows are always nice. Unfortunately, Orianna does not really take advantage of the slow part of item. The slow is only a 15% debuff because all of her spells have an AoE. Besides, Orianna already has a slow in the form of her W.
Will of the Ancients: This item would be optimal for all AP champs, but Orianna simply does not benefit too much from it. As a support you need to have the team's best interest at heart, but there will most likely already be another champ with the item, so you really shouldn't bother unless your AP champ refuses to take this item for some reason.
Haunting Guise: Who the hell uses thi- I'm not too big a fan of this item. If you really want the minimal benefits it offers, go ahead. I would only take it early-mid game and sell it in favor of something more useful, like say, a ward.
Banshee's Veil: Someone suggested I take this item once. I found it absolutely useless on Orianna, since she is very capable of escaping if ever caught alone (which should never happen), and she should not be getting attacked to begin with because you should be protected by your team. If you ever think you NEED Banshee's Veil, you are playing support wrong.
As a support character, this is the single most important item in the game for you. Wards provide visibility, safety, and stop ganks in their tracks. Dragon and Baron control are also benefits of proper warding.
Here is a very good guide to wards.
Always take your Q first. Why not your E, you may ask?
Well you see, Command: Attack is essentially a free ward. This trumps Lux's Lucent Singularity because it costs less mana and the Ball stays in place, so you don't have to spend a ward on the bushes in your lane. Always use your Q to bush-check.
Orianna's Ball is a fun little tool for harassing before team fights. Although it's damage is piss-poor, it still does a little bit of damage and grants some visibility as to what is happening ahead of you. When are your other spells are on cooldown, you can use your Q to deal some damage in team fights, unless you have a shield target.
Remember, you can stay a good distance from your ball before it teleports to you, so use this to your advantage.
Take your Q first and max it last.
Take this at level 3 and max it after your E.
Command: Dissonance is a nice AoE spell that speeds up allies that pass through it and slows enemies as well. It does damage, but it's not too remarkable.
Use this spell when you need to get somewhere in a hurry, as the speed buffs you up to 40% extra speed and slows enemies for the same. Use your E on your AD carry or damage dealer followed by your W and watch the enemy champions flee in fear. This works nicely on Vayne, Nocturne, Volibear, and Kennen.
Command: Dissonance is great for halting ganks in progress. Relocate the ball to yourself or teammate who is in distress and press W. Your teammate will have a speed buff and the enemy champs will all be slowed. You can also use this to your advantage when being turret dived. Pair your E with your R, and the turret will wail on your would-be attacker without mercy.
The Reverie with Command: Dissonance will make you and your teammates unreachable.
Orianna's bread and butter.
This spell makes your ball stick itself onto a target and grant them a small shield for a while. The ball's passive grants a very nice Armor and Magic Res buff that applies as long as the ball is on the target. If the ball is called onto a target and it passes through enemies on its way, it will deal some minor damage.
You should always keep the ball glued onto your main damage dealer or initiator (if not the tank) for max protection. If someone else needs protection, you can easily swap the ball onto another target and speed them up with your W to help them get out and get the ball back onto the main damage dealer.
This is without a doubt your most important spell. Take it at level 2 and max it first.
This spell is what makes Orianna so great.
The spell has a surprisingly large AoE compared to Command: Dissonance, which can and should be used for your team's advantage.
Orianna's ult is second to none in terms of disruption. Although Janna can blow the enemies away or spin them in place, Orianna instead suppresses everyone within the spell's radius and makes enemies caught within it jump to the opposite end they were caught in. This means that in teamfights, you can swap out the tank and AD carry for the squishy support and AP Mages in the back for easier focus.
Be careful when using this though.
You can accidentally get yourself and your team killed with this spell. If you accidentally bring IN the tank and AD carry, your team might have difficulty winning the battle. Luckily, Orianna is an escape master.
This spell is optimal for almost every support. Specially for Orianna, since she is a support without a healing spell. This is a good early-game spell but will piddle out by mid-game.
Orianna is the queen of visibility, and needs this to have absolute map control. Constant supervision of the enemy jungle and watching for possible ganks when wards are not up makes this spell a must.
Other Viable Spells
Clarity: Orianna is a very mana-hungry champion in the early game, so this Clarity can help you stay in lane longer. Very useful if your team is very mana-reliant.
Flash: If you are not comfortable getting within the range that Orianna needs to be in to be effective, Flash is a nice escape option. But you already have a nice escape mechanism in the form of your W, so this should only be used by beginners.
Teleport: This is very helpful to get back in the action quickly. In the words of Dunkey: "If you're out of the loop, you're out of the mix and if you're out of the mix you don't know what's going on." You can use this to teleport to wards and help a teammate in case of emergency.
Not Useful on Orianna
Cleanse: There really is no need for this spell unless you're going to be getting up close and personal, like Kassadin would. You are not Kassadin. You don't need this.
Exhaust: You already have a built in slow with your W with a much faster CD.
Ghost: You already have a built in speed boost with your W with a much faster CD.
Ignite: You're not really going to be last-hitting anything, so this is not too good on support Orianna.
Promote: Who the hell uses this?
Revive: Unless you're Dunkey or really, really, REALLY good, no.
Surge: Orianna is capable of being a burst champion, and this would help her in that. However, this is a support guide.
Orianna vs other Supports
Orianna IMO is one of the better supports in the game. But how does she match up against the other contenders with similarities to her?
Janna vs Orianna
Janna is very good at a lot of the same things Orianna is.
They are both capable of disrupting team fights, both have slows, both have a speed buff, and both have a shield.
Janna's disrupt potential only either holds enemies in place or blows everyone away. Orianna on the other hand, can shift the line-up at the touch of a button and shred through the supports and squishies hiding in the back just as the tank and AD come back in to try and win.
Janna's slow is very nice and is precise, while Orianna's requires her pursuers to step into its AoE to be effective. However, Janna's speed buff only boosts by a small percent, although it is global. Orianna is better at escaping with her team at the drop of a dime though.
Janna's shield is very short lived and does not grant the armor and magic res buffs that Orianna's does. However, it is usable on turrets.
Both champions have great map control and visibility. Janna's speed allows her to drop wards everywhere quickly, while Orianna is a little slower. However, Oriana can bush check without a risk with her Q.
Orianna vs. Karma
As a Karma player, this comparison is going to be very tough. Let's try anyway.
Both characters have a shield and a speed buff/debuff. Orianna wins on both accounts, unless Karma activates Mantra. In that case, Karma will always win the support battle.
Karma is an odd support AoE burst champion that can both heal and deal absurd amounts of damage on low health. However, she is very reliant on Mantra to do most of the promised burst damage. She also lacks an ult to help in battle. In a normal situation, Orianna will trump her in terms of defensive play. Karma does have the advantage of having a heal to keep her lane partner going and her speed buff lasts longer.
Orianna vs Lux
Although I think of Lux as more of an AP Mage, she can still support pretty nicely. Lux deals more damage than Orianna, but Orianna's support is way better.
Both have a shield and slow. Lux is even more mana-hungry than Orianna, so that should say something... Orianna's are both better simply because they cost less mana, are less likely to kills steal, and have more benefits.
Shortest review yet. Yay!
Orianna vs Sona
Sona is the Tryndamere of supports. That being said, she gets banned all the time in Draft.
In ordinary games, however...
Both have a speed buff, and that's about all they have in common. Sona's is shorter lived but remains in an aura. Orianna's is faster and can be used almost as fast as Sona's. Both are equally matched in this department.
Orianna vs Zilean
Orianna is a great support and doesn't afraid of nothing.
Skill Priority: E> W > Q
Take Q at level one and leave it
W at level 3 and max second
Q at level 2 and max first
Items: Ionian Boots, Soul Shroud, Abyssal Scepter, Archangel's Staff, Shuryelia's Reverie
Heal + Clairvoyance
Hate Zilean all day every day