Janna Build Guide by
Not Updated For Current Season
(Please excuse me if I manipulate the English language awkwardly, you may leave a comment if this becomes confusing.)
In my opinion, Janna is the best champion in League. She will seldom win a 1v1 encounter, but can make a 2v4 possible (and quite safe if your carry knows what he's doing!).
I have been maining Janna since season 1. You're about to receive insight which you wouldn't expect from the title of this build! At first, I played a mana regen/movement speed intensive build for about 5 months. That's when I learned to use Janna increasingly effectively. I then switched to the (once somewhat popular) Janna AP mid (or support in many games) path for about a year until her Q's damage was first nerfed. I then gradually brought myself to play her as a conventional full support. Then once, I implemented the old item Force of Nature (for those who don't remember it, it granted a large amount of magic resistance and movement speed along with a stronger version of the current Warmog's Armor passive) against an magic damage heavy team. My life was changed. I started building weird items like Randuin's Omen, Banshee's Veil and other items of the like and actually did very well with them!
So, while this guide probably isn't going to suit someone who wants to pick up Janna, people who are used to her early game weaknesses will catch onto it rather easily. There is much to say about positioning and certain match-ups that I won't touch in this guide, except the parts where it is more effective to play her different from usual. So, let's begin!
You will want either 0/9/21, 0/21/9, 0/0/30 or anything in between which pleases you. This is why I won't even bother putting Masteries up, but I went from 0/0/30 (at the beginning, when I was building full support and changing into the lategame tank build) to 0/9/21, to 0/21/9, and have now been back to 0/9/21 for almost a year. This is how I prefer it, and even though it isn't useful every game, I pick up the buff duration Mastery because I love having that extra power on her and I tend not to die and give the buff to the enemy team, though when I do, often enough my team will clean up the fight because I died for us to win said fight.
Used to use all of the gold runes with armor reds and magic resist blues. Not anymore, since the ambient gold changes. I pick either physical damage or armor Marks, armor or health Seals, magic resist, magic resist per level or cooldown (less preferably) Glyphs and health Quintessences.
This one definitely changes from game to game (the order in which I build items anyway). I'll start with either Doran's Shield and a mana potion if the enemy bottom lane is auto-attack harass heavy, or more typically, an Amulet Coin, a green Ward and two Biscuits (pick one health potion and one mana potion if you don't have the biscuit Mastery). You will also want the Warding Totem Trinket.
Spell order is ALMOST always E-W-E-Q-E-R-E-W-E-W(max R then W then Q for last). When you encounter Thresh, Leona, Braum, Tristana or Blitzcrank, perhaps you will want to get your Q at level 2, but keeps maxing E and get W at level 4. This is to cancel Leona's E (if you're fast you will be able to stop her from jumping onto your carry which is her primary goal), make Blitzcrank or Thresh's Q kind of moot by knocking both enemies up at once if someone is pulled so that they can't follow up on the Q, or stop Tristana mid-track when she jumps if someone on your side is very low already and she decides to go for the very early kill (otherwise, get W at level 2).
You will want to play Janna as per usual since you really aren't much (if at all) tankier than the conventional builds at this point. Assess what the enemy lane can do, how the enemy jungler travels the map, make sure you have wards up when you don't see him. Keep the bottom brush(s?) warded if Blitzcrank, Thresh, Leona or Braum is the enemy support. Otherwise ward them when necessary.
Your goal is to aid your AD Carry win trades. If he is injured at all and one or more enemy is low on health, this is where you start acting like the Janna I play (and this is even more effective from level 6). You will taunt the enemy into attacking you for free until your AD Carry starts hitting a target. You will then knock them up and slow them, shield your injured carry, back off (they will either run or attack your carry which you should have shielded from the moment he attacks), and if they turn to attack your carry, run quickly back into the fight and use your almighty auto-attacks. Since you are low, there is a chance they will turn back on you. Bait them (meaning keep playing the poor weak and helpless Janna) until you are dangerously low, then Flash. If your Flash isn't up, run a little earlier OR keep an eye on your cooldowns and use something to get away.
If you are level 6, this is much easier. You're slightly more healthy than the typical Janna, so to use it properly, once you are somewhat low on health, Flash at a critical time between your targets (might be when your jungler arrives) and split them very far appart, where one cannot help the other. Bonus points if your ADC is in the heal aoe. Channeling her ult is optional/situational (probably a good idea if your spells are on cooldown or if your ADC might lose the fight vs whoever is on his side of your ult). Note here that you want to split them as horizontally as possible, not vertically, since their spells with range will start attacking your ADC a second later which is what we're trying to avoid. This is a form of "Peeling").
If victorious, and if your jungler is nearby, see if your team is ready to take a Dragon. Make sure wards are up if the enemy jungler wasn't in the last fight, then proceed to let your ADC free farm/hit enemy turret a few times. Maybe they'll just want to back, and that's their right.
Going back, you will want either of 3: if you have the gold, purchase Mejai's Soulstealer AND wards. Janna is a great champion to carry Mejai's Soulstealer because she is hard to kill. Harder yet with this build. And a VERY strong argument to pick this is, when you get many stacks on Mejai's, enemies will want to kill you ASAP. And you are the Bait Queen. This build reinforces this in every manner.
If you don't have 1300 or more gold on your first back (more than likely, you won't), but have over 800 gold, you will want to buy the Sightstone and a few biscuits/potions. No more wards, some more health, a very good purchase.
If you have less than that, something went wrong in lane (it is possible that your ADC is really bad, but you shouldn't die. You should VERY rarely die, in fact). Buy Nomad's Medallion AND wards/biscuits/potions if possible, but if you couldn't afford wards with the Medallion and ran out of wards, forget it. Buy Boots if need be, and most importantly, wards.
By the end of early game, you will want all of these items anyway. Get them all. Except maybe in some cases you can forget the Medallion and end up selling the first piece at the beginning or end of Late-Game (if for instance Sivir is on your team, because her ult acts like the Talisman of Ascension, final item in that item tree).
You will also want to swap your Totem of Warding for a Sweeper Lens.
You will want to start warding deeper in enemy territory, and doing so as safely as possible (so use the maximal range you can when placing wards, stay as briefly as possible, do it when you're following someone, do it when you see most enemies, etc). If your ADC is the type to become stronger late-game comparatively to the enemy ADC, one good option is to have him farm bottom lane as long as possible. If your mid laner has a good synergy with you, by all means, go gank for him (also check if the enemy mid laner is likely to be able to run away from slow, tornado and ult (if it's up) so you don't waste your time/mana). You may want to keep protecting your ADC in lane if the enemy team has a lane bully like Blitzcrank. Once their tower is down (your might fall first, keep going just make sure to keep warding and to keep an eye on the mini map for your allies), get Dragon with your jungler if it's ready (ward accross the wall from the opposite side of the entrance to make sure enemy jungler isn't waiting to steal it). If not, go for mid lane turret.
Assess enemy team. Consider your next item carefully. Building any of these is viable in most scenarios, but often one ends up being better. Either build Mercury's Threads (to be very hard to catch!!! So very hard!), Warden's Mail (mostly if enemy is heavy on physical damage or you're staying bot lane and enemy ADC hurts a lot), Spectre's Cowl if enemy support deals a good amount of magic damage, nemey jungler deals magic damage, or if you're thinking of attacking enemy mage middle laner before returning to lane. A note on this: Janna is very mobile, so she is one of the better supports to gank with her strong Crowd Control (CC) ability. Keep enemy mid laner as far as possible from their turret for as long as possible while shielding the target of enemy attacks to give your side an edge. Appear from near enemy tower and blow them away! If you're successful, your ally will probably get a kill and push the tower (warding is a good idea to prepare for retaliation).
Mid and Late-Game Purchases
All along if you bought some Vision (pink) Wards you've been doing the right thing. Keep it up unless your inventory is full.
Build Randuin's Omen as fast as possible, but make sure you have at least the Negatron Cloak or preferably Spectre's Cowl by then. Sometimes, just the Mercury's Threads are fine, though. After that, either finish Talisman of Ascension if it's nearly late-game, or Banshee's Veil. You will want both, but you may consider switching Banshee's Veil for a Locket of the Iron Solari (not recommended by me unless there is an enemy Karthus and/or more AOE (Area of Effect) magic damage dealers your team tend to die to). The point of Banshee's Veil is this: you get a free spell block which will allow you to Flash+Ult without failing as easily. It is ultimately better to do so than grant your team a mediocre shield. Your ultimate (a proper one at least) may win the fight on its own. Try to single-out low-survivability champions that can wreck your team (or sometimes a Legendary enemy).
After all this, you should be able to take some pain. Now for the fun part!
The Fun Part (or Late-Game and Teamfights)
You are now very mobile (and so is your team if you have Talisman of Ascension). Pick the right timing and fight with superior vision. Siege enemy towers with your team if you like AND your team is ahead. Q someone, wait for more CC to come from your team, Flash in and ult, or, wait for enemy team to engage, screw their positioning, get low on health and bait to further screw their positioning as you are focused, speed up your team or slow down theirs with your active items, and reap the rewards.
Often times, in mid and late-game, you will be about a fifth or less the map's distance to your allies. Look for enemies. If you find one and are about half health, here's the kicker of this build: have enemy(ies) try to chase you down for the kill, somehow make them believe they will get it, then last second use whatever tool(s) is/are left off cooldown to get your allies to chase them hard in a bad spot (for them). This usually results in a kill or two. Proceed to push or get neutral objectives with your teammates. Sometimes you may even initiate a full-blown teamfight this way! That is the best for you.
Note on shielding yourself: with the resistances (physical and magical) you have with this build, more often than normal, it is good to shield yourself. Stay in the front line of your team with your actual tank or another bruiser (you may be the main tank) and keep messing with their positioning/highlight targets that are prone to dying for your team. With practice you will get to a 70% winrate with Janna as I do! So long as someone on your team knows what they are doing better than the average of the enemy team, you're golden. Good luck, have fun!