This section of the guide is devoted completely to the 3v3 Twisted Treeline map, and is part of Shining Light on Leona, an in depth guide to playing Leona, which can be found here: http://na.leagueoflegends.com/board/....php?t=1000951
Leona is a very potent 3v3 pick given the proper team composition, and I will explain some of the key differences you will need to make to your play style and builds. The information in this section is only added as I myself personally test or encounter it. I encourage questions you have about TT play with Leo to be posted on this thread rather than the original.
Skill order on this map is more straight forward, as your role is Damage and Control. I level Q first, taking points in R whenever possible, and leveling Zenith Blade secondly. The reduced cool-downs and increased damage on her main CC skills allow her to thrive, though you must remember you will not absorb nearly as much damage as normal. You can alternate Zenith with Eclipse if you feel you will be doing more tanking than anyone else in the group.
Masteries, Runes, and Items
Leona's masteries differ greatly on this map, as it is important that every member of your team be able to contribute good damage. Because of the nature of the map, ganking, burst damage, and control are much more important to have in your team's compositon. Fortunately, when properly built, Leona can contribute large amounts of all three of those things. As such, I have found the best success with a 21/0/9 build, improving Exhaust and taking all forms of physical damage increase. Armor Pen, Flat damage, etc. You can take increased crit damage if you feel you will want to build crit chance. Grab the increase to EXP and death time reduction in Utility, with 1 point in increased buff duration. It is also possible to use 21/9/0 to grab Nimbleness if you feel the dodge will help and plan on taking dodge seals / quints.
On a side note, Leona's Default tank masteries can be used on this map, but her already low damage out put will be so low on this map that it's not likely you will get kills for your team. While that is not normally her job, on 3's it is important that Leona can contribute damage and kills.
The runes I use for Leona help to compliment her offensive Masteries as much as possible.
Red: Armor Penetration Marks or Flat damage Marks are the ones I have had the most success with on this map, both of which are about tied. Unless you do ranked, you're not too sure of who you will be up against, and since very few people tend to start with anything other than base armor, the flat damage when stacked with a level 1 Doran's Blade is just as effective as armor pen. For offense your only other option here would be Magic Penetration, which is useful if you build as much early spell pen as possible to stack.
Yellow: Yellow Seals I take for TT are MP5/Level. Because of the skirmish nature of the map, Leo can run out of mana much faster than on Summoners Rift. These seals help to counter-act that weakness. Other options include Health Per Level, Armor, and Dodge if you want to grab Nimbleness out of the defensive mastery tree.
Blue: Flat CDR Blues have shown me the best results of everything I have tried for this map. It has literally been the difference between killing someone, or being killed. Flat AP or AP/Level can be used for those of you planning on building AP items, and Flat MR can be used if you stick with her tank build.
Purple: Armor Penetration or Flat Damage Quints should be stacked with the same one you pick for your Marks. The only other exception would be Spell Penetration of flat AP if you plan to be more AP based. Defensive options include Armor, MR, Health, and Health Regen. The flat Health can be used to make you slightly less likely to be targeted if your team attempts a level 1 gank (which many pug groups do).
It is important that you plan what you want to do from the very start of the game using your Mastery and Rune build. Your level 1 item pick should reflect this plan as well. I have had the most success starting with a Doran's Blade. The increase to your health and damage are very strong, given the nature of her Q's ability to allow 3 attacks in under 1 second. This gives very good physical burst during a low level gank.
Your TT build should be very offensive in nature. The build I use is as follows: Doran's Blade x 3, Boots, CDR Boots, Sheen, Phage, Tri-Force. More times than not, the game is going to be over by this point. I've had matches in which I rushed an early defensive item, buying only two blades and skipping Sheen until it was completed, but the general idea of this build is to allow Leo's toolkit to be used as an AD Melee carry. Her kit is very well suited to this, but you should bear in mind that you won't be nearly as tanky as the build detailed for SR play in this guide.
Her AP build differs a bit, but has the same general principle. In my experience, I have seen less success with it, but I have been able to win games with it, even as the carry of the group.
AP Build: Doran's Ring x 2, Sorc Shoes, Haunting Guise, Sheen, RoA. Game tends to be ending by this point, if not I go for Lich Bane, selling rings towards Death Cap, and Abyssal Scepter. You can alternate the Haunting Guise for Malady if you feel you won't be prevented from auto attacking often enough for it to penetrate better than HG.
Flash is considered a must by me and probably many other summoners that play TT often. It is invaluable in escape, and can be very useful to chase someone, especially if they have flashed to attempt an escape.
Exhaust is the second summoner spell which I take almost exclusively on this map. Combined with flash, you have huge amounts of utility in your spell usage, balanced between offensive and defensive. Exhaust also enables Leo to 1v1 far better in certain situations, which can be hard for her and is more common on this map.
Ghost, Heal, and Ignite are also very good picks for this map. Ghost is very common use, Heal can be helpful in 3v3 skirmishes to stop yourself and allies from instantly dieing, and Ignite is free damage.
If you feel like you'll be against a strong CC comp, Cleanse is a wonderful choice, and should be stacked with a Quicksilver sash.
Playing Twisted Treeline is far more offensive, fast paced and gank oriented than 5v5. Because of this you need to think and act quickly. As soon as you spawn, purchase your starting items, and comminicate with your team on wether you feel comfortable trying for a level 1 early brush gank in a lane. You should make this choice based on your team comp VS your enemies. Teams with lots of mobility and / or control and burst are far stronger at level 1 than others. Leona provides burst and control, but not much mobility at level 1. As such she is a good level 1 ganker, but it takes 3 to tango in this forest. Your first spell should be Shield of Daybreak, I've never had a reason to take Zenith Blade or Eclipse before that on this map. You get the most bang for your skill point out of her Q.
Pre-6 should be spent last hitting, or harassing hard if you have a good lane partner for it. Taric, Ezreal, Mundo, Annie, people that can spam skills that almost always assure lots of damage when combo'd with Leo are good examples of harass lanes. On the rare occasion you end up solo, play defensively. You will likely be pushed to your tower, so do your best to last hit under it. Thanks to your offensive Runes, Masteries, and early Dorans Blade, this is not nearly as hard as it would be otherwise.
If your team has lots of mobility and burst, try to coordinate early ganks. In the least this lets you keep track and control of the jungle, which is practically the entire map. Leona makes for a very good ganker on this map. If you have a jungler this is particularly easy, and if your opponents team has one you should look to keep track of them and make their life hard, or you could regret it.
One you get your ult, your team has a considerable range advantage. It's large cast range allows it to initiate well, or prevent people who flash poorly from getting away. You will need to be a little cautious with it's use though, as you want to hit everyone you possibly can. By level 9, you should have your Blades, and boots. If you are doing well, you may have finished Sheen or have items towards a defensive item. Now you should be constantly traveling as a pack, warding, and keeping control of Dragon and Lizard, as well as the other neutral buffs. Green buff is powerful on Leona for the CDR, though White and Red should typically be given to someone else. Downing Dragon gives large gold and damage advantages.
It is rare for a TT match to last past the 20 min mark, though if it does you should focus on finishing your items by farming or forcing team fights. Your team should always focus the highest threat targets, which are typically burst casters or AD carries. If the entire team is AD carries (which happens alot), pick the one with the least defensive options / stats. If you're facing a hellish comp, such as Mordekaiser, Yorick, and Jax, try to keep one of them under constant control so they can't rampage through you all. That is one example of a team that is difficult to defeat in team fights, so when you come across those, you should also look to split them up and focus them down whenever you can. The rest of the game play for this map comes with experience, just remember that wards are your friend and that the team controlling the jungle is usually the one winning.