Hello everyone, and welcome to my Shaco build (Why Clowns Scare Me). In this guide I hope to cover everything about how I play Shaco, and hopefully help other people get the gist of him as well.
Overall, Shaco is a balanced melle DPS champion, who uses his abilities often, but does not rely on them to win fights. There are several ways to play Shaco, (like DPS, AP, etc.) but I've stuck with DPS. This build was originally made for a 5v5, but I believe that it would work well in a 3v3 due to Shaco's total dominance of Twisted Treeline.
I hope that this guide helps you all learn about The Demon Jester!

For runes, I take Greater Mark of Desolation marks (+1.66 armor penetration, total of 14.94 bonus armor penetration), Greater Seal of Alacrity seals (+0.76% attack speed, total of 6.84% bonus attack speed), Greater Glyph of Malice glyphs (+0.28% crit chance, total of 2.52% bonus crit chance), 1 Greater Quintessence of Swiftness (+1.5% movement speed) and 2 Greater Quintessence of Wisdom runes (+2% experience gained, total of +4% experience gained).
These Marks are a HUGE help in games, especially early game. As it is flat armor penetration, it can make negatives, and if not, it still makes it a very small amount of damage reduction, especially on minions, making him a great farmer (see Farming below). Also, it makes squishy champions even squishier.
I take the Seals of Alacrity for the extra bonus in attack speed. These also make Shaco powerful early game, allowing him to gain dominance in the game. The attack speed also gives him a slight advantage late game.
The Glyphs of Malice are especially helpful late game, although they do have an impact early game. The extra crit chance is great with the rest of the build, especially when you get your Infinity Edge. It also helps with early game farming.
His quintessence are all not definite. There are defiantly other quints that could help Shaco, but I take these because I feel they give him more dominance and control of the game. The extra movement speed from your first one helps him get in and out of battle easily, as well as chase down people. The extra experience, combined with the other bonus that you are getting from your Utility masteries (see Masteries below) give Shaco a great amount of dominance in the laning phase, and make him stronger faster. This also gives him an advantage early game as he is more powerful than everyone else.
Overall, I think that these choices in runes make Shaco a dominant champion early game, thus making him get fed, and stay powerful throughout the game. I take only flat bonuses in my runes so that they are stronger early game, and he levels up MUCH faster than everyone else. I believe that with these masteries, and farming skill (again, see Farming) he gains dominance in the entire game.

For my masteries I take 21/0/9, with the summoner spells Exhaust and Ignite (see more on this on Summoner Spells). You can see everything I take in detail above. The bonus offense helps him immensely, especially early game. While offense is pretty much self explanatory, one my utility choices may seem strange, and that is to get Greed, instead of something like Utility Mastery. In my opinion, I don't think it matters much. I find Greed a good help to give Shaco more power, as he is somewhat dependent on items. However there are manny good things about other Utility options, especially if you use the jungle a lot. I personally only go in there ocasionaly, so I get greed. However, the choice is completely up to you.

My item build is probably the biggest part of this guide, so I ill try to explain my choices as best as I can.
I start the game with a Sapphire Crystal and 2 health pots. Some people might argue that Shaco should get a health and a mana pot, but I find that the Sapphire Crystal is usually enough. Also, the second health pot is more beneficial than a mana pot because it keeps Shaco from dying, and allows him to farm with ease, while a mana pot make him able to harass, but farming is usually more important early game, especially with Shaco as he is so dependent on items.
On my next time back, I try to be able to get a Sheen and at least level one boots, if I can't get Berserker's Greaves. The game suggests that you get boots of mobility, but I think that Berserker's Greaves give Shaco more damage output, and therefor makes him stronger than his ability to escape. Also, his runes and other items solve his movement speed issues.
After that a get a Madred's Razor, then first getting a bow before the pickaxe. The extra attack speed is crucial.
After that, I up my Razor to a Bloodrazor, and then immediately get a vampiric scepter. At this point in the game, Shaco is very squishy and has very little health regen. Getting a Scepter gives him enough survivability for a long time. If you find that you need more lifesteal, then you can up it to an Executioner's Calling that you can sell later in the game if necessary, so you can get more lifesteal and some more crit chance.
After that, I get a zeal, and then up it to a trinity. It's usually endgame by now and trinity force is probably the best item you can have to go along with the other items in your build. It gives more attack damage and health, which are welcome, and just about everything else you need except for lifesteal, which is covered by your Vampiric Scepter.
The next 2 items tare Phantom Dancer and Hextech's Gunblade. Both of these items are great, especially late game, so the order in which you get them doesn't matter. Most games are over by the time you can get one of these. What you choose is dependent on the game. If you are being a more hit-and-run Shaco, you should probably get a phantom. If you are doing more 1v1s and chasing down, a Hextech's is probably what you need.

REMINDER: This build is a guideline and is not set in stone. Depending on the game, you may want to change it, majorly or not. For example, if the enemy team has no tanks and is mainly a mana based team, you might not want a Madred's and could get a Wit's End instead.

My skill sequence is the least definite of everything in this guide. Everything you get is situational. I like to start with Two-Shiv Poison, but many other people argue that Jack-In-The-Box is better. ITs completely your choice. I level up 2-Shiv first, and get points in Jack in the box early, and get more in Deceive later in the game, when I find it is more useful. However if you want to reverse these, that's fine. It all depends on how you play Shaco. Obviously, I get Hallucinate whenever available.

For summoner spells I take Exhaust-Ignite. I can already hear some people going "WHAT? NO! Ghost and flash, or one of the two, get them or DIE!!!!" I find ghost and flash both adequate on shaco with either Exhaust or Ignite, or even something else. However, I stick with Exhaust-Ignite for several reasons.
First of all, Exhaust, is MARVELOUS in chasing people down. If you can get it on them after a Deceive, and then hit them with 2-Shiv? It's a fantastic combo! If you can also get an ignite on them, your almost guaranteed to get a kill of at least deal a lot of damage to the enemy, making them weak. So while I have nothing against ghost or flash, I find that Exhaust-Ignite is the best on Shaco.

PROS:
1. Grants Shaco some survivability.
2. Makes Shaco very strong early game.
3. Gives Shaco great assassin and ganking possibilities.
4. Gives Shaco FANTASTIC DPS potential.
5. Gives Shaco great maneuverability.
6. Makes Shaco become stronger faster than all other Champions.

CONS:
1. He is still VERY squishy.
2. He is bad against people with armor.
3. Relies heavily on Shaco's ability to farm early game.
4. Requires a lot of skill in ganking and map control.
5. Requires at least somewhat good allies.
6. Shaco, as a champion is often targeted because he is scary. I can't really figure out why else. Shaco has very little defense.

So it all balances out. If you can farm well, avoid feeding, and get enough kills, this build will help you crush the opponent. If not...well you might have a little trouble friending your teammates.

Shaco is a very powerful assassin, 1v1-er, hit and runner, and he is the king of 3v3s.
His assassin abilities are fantastic, and he is great at showing up, ganking, killing, and blinking out again. His 1v1 skills make this better, and he has great escape potential. All of his skills combine to great great combos and making him powerful. Also, if you have some skills, you can become a great farmer, which allows him domination.
Finally, he just WINS twisted treeline. He can get between top and bottom lanes easily, and KILLS EVERYTHING! With a small amount of skill, you can get a big advantage. With a lot of skill, you are almost GUARANTEED to win the round.

This is one of the most important parts of this guide, but it is one that I can only give a little guidance on. To farm, you have to be good at last hitting, and have good timing. However, if you can get this right, you get a huge advantage. If this combines with everything else in this guide, you become pretty much unstoppable. You get levels, power, and items before everyone else. This will give you the advantage to win the games.

Overall, with all of this, you will become OP! Shaco will strike fear in the enemy's heart when they see you, and they will run in terror, but it will be too late! You will win super-fast, and kill everything. Have fun out there!