Welcome to my first Mobafire League of Legends Champion Build. It's still not finished and i'll be editing as I go.

Master Yi plays the role of an Attack Damage Carry. He's meant to massive physical damage and carry the team to victory. A basic team composition rule is to have an AD Carry, AP Carry, Support, Tank, Off-Tank. If Master Yi is build around a team with tons of CC, then he's going to have a fine time picking off people with his DPS. Don't forget, if you play Master Yi and get dropped as soon as you walk in to battle, your team will surely lose. An AD Carry is needed to be alive during team fights to ensure the opposing team actually dies! As soon as the AD Carry drops in my team, we push backwards and switch to defense. All teams play differently, but an AD Carry must be smart on when to initiate and when to not!

Pros:

Great Jungle Champion
Great Ganking Potential
Strong DPS
Very Fast Champion
Great Escaping Ult
Potential Penta-Kill

Cons:

Squishy
Low HP
Usually Focused
Useless if Blind, Stunned, Exhausted, Snared...
Easy to Counter ( Thornmail, Frozen Heart, Randuin's Omen...)
Champion Counter ( Teemo, Rammus, Jax...)

Don't let the cons listed above sway you from using Master Yi, he's a very powerful Champion that's underestimated.

Smite:
For my first spell i grab Smite for jungling. Master Yi is quite a squishy character, without smite he can't jungle as well as a jungle Champion should. It speeds up his jungle speed and ensures counter-junglers can't steal your buffs.

Ghost:
Secondly, i grab Ghost. Now Ghost is a superb skill for Master Yi, giving him the speed needed to catch nearly any Champion that he's fighting. He does have Highlander and Youmuu's Ghostblade, but image the devastation of combining Ghost, Highlander, and Youmuu's Ghostblade.

Other options can include Ignite, Flash, Cleanse, Teleport which are all worthy if it fits your playstyle. If I keep getting CC'd on previous games, i pick up Cleanse for a couple of games.

Greater Mark of DesolationGreater Mark of Desolation:
Now i grab 9 x Greater Mark of Desolation for early and late game armor penetration, it helps early game by penetrating Doran's Shield. Throughout the game, it gives the armor penetration needed that people WILL pick up.

Greater Seal of Resilience:
Since this Yi build is for Jungling, I grab 9 x Greater Seal of Armor. It gives Yi the necessary armor to jungle at early levels along with enough armor to survive during ganking. Combined with Wriggle's Lantern, Yi can have enough armor to survive for most fights, if played smartly.

Greater Glyph of Alacrity:
Now my glyph set of runes, 9 x Greater Glyph of Attack Speed, are generally personal preference, but it helps greatly during early level ganking and jungle. It gives Yi the extra speed needed to hit his passive Master Yi Double Strike. This can be switched out with cooldown runes or magic resist per level.

Greater Quintessence of DesolationGreater Quintessence of Desolation:
For my quits i use 3 x Greater Quintessence of Desolation, it gives Yi that armor penetration that will last throughout the game. Definitely the best Quintessence for Yi.

Jungling items for any character is pretty similair. You start off with a Cloth Armor and 5 x Health Potion. These are the basic items needed to Jungle with Yi.

Once the first jungle route is completed, you should have roughly 500 gold. I return for a Boots and return to the jungle. Golems should have re-spawned by now. After i take down the Golems, I pick a lane to gank while having the Red Lizard Buff.

I return to purchase a Madred's Razor, this item helps you jungle 100000x faster. Once the next route is complete, i return to build a Wriggle's Lantern and Berserker's Greaves. Now Wriggle's Lantern is a great item for Master Yi in this build, it's KEY. Free ward for the entire game (until it's sold at late game for a stronger item), Lifesteal, AD, Armor and the awesome 20% passive for jungling.

Next i grab The Brutalizer giving me enough AD, ArP and CDR to return to the jungle and continue ganking. After some more jungle rounds and ganks, i return for a Zeal giving me AS, CSC and MS.

All these items combined, we are Captain Planet! but seriously, I return for a B.F. Sword giving me a ton of AD, then continue building it to an Infinity Edge.

After i build the IE, i come back to complete the Phantom Dancer giving me more AS, CSC, and MS. At this point, Master Yi should be unstoppable. Finish up the Youmuu's Ghostblade and grab any final item that would fit the scenario.

Madred's Bloodrazor:
This item is great for HP heavy champions such as Cho'Gath, Nasus, Mordekaiser and Champions who build with Warmog's Armor

Sword of the Divine:
This is used specifically for dodge heavy champions such as Jax or anyone who uses Ninja Tabi

Wit's End:
This is great if you're struggling to fight AP champions such as LeBlanc Karthus or Akali. It provides MR, Deals MD and Procs with MR.

Executioner's Calling
This item has a great active for regen heavy champions. It gives you Crit and LS, with an active that only has 20 seconds cd. This item is used to stomp out Dr. Mundo Swain or any other Champion of the sort. It's also used to stomp out physical lifesteal champions who use Zeke's Harbinger Bloodthirster Hextech Gunblade

Last Whisper:
Last but not least, the Last Whisper. This is a wonderful item for champions who stack armor. If you see a Randuin's Omen or Frozen Heart, don't hesitate to get this item.

Banshee's Veil:
As Master Yi, it's essential to enter in a fight without getting snared, stunned, or blinded. If the opposing team has a couple CC's and you consistently find yourself getting trapped, pick up a Banshee's Veil. The cooldown on it is beautiful and also gives HP MP and MR.

Guardian Angel:
This item is usually underestimated on Master Yi, generally because he's a squishy character. Now it gives a noble amount of MR and Armor + an awesome passive. If you find yourself CONSISTENTLY being focused, grab this item. It can bring you back into the fight after the focus has shifted so you can get back into the fight and land some DPS. This item doesn't work well if your team leaves you to revive in the enemy team's grasp.

Quicksilver Sash:
One of the most underestimated items in the game. It provides with a good ammount of MR as well as an awesome active. On top of that, it's really cheap! If the opposing team has a couple CC's, don't hesitate to get this item! A CC'd Master Yi is a DEAD Master Yi. Imagine if you're being Nether Grasp, it can easily be stomped out by this item!

First Route:

Start off with a Cloth Armor & 5 x Health Potion, then head out towards Blue Golems. Once you're there, AA the Blue Golem and immediately Alpha Strike the group. Use a Health Potion as soon as you get hit. Continue to AA the Blue Golem and use Smite to finish it off.

Once you finish with Blue Golems, continue to wolves. AA the Big Wolf, then immediately Alpha Strike the mob.

Continue to Wraiths and AA the Big Wraith, immediately after the AA hits, Alpha Strike through the mob. Activate Wuju Style and continue to AA the mob. Alpha Strike whenever CD resets.

Use Health Potion to keep your health up, AA the Red Lizard and Alpha Strike through the mob. Activate Wuju Style and continue to AA the Red Lizard. Repeat until Smite is back and use it.

Continue to Double Golems and AA one Golem, then Alpha Strike through the mob and activate Wuju Style. Use the last health pot and continue to AA.

Return to base and grab a Boots, some Health Potion and Sight Ward, then find a juicy lane to gank.

Second Route:

Head out towards Double Golems with a Cloth Armor & 5 x Health Potion. AA a Golem, following up with an immediate Alpha Strike. Use a Health Potion as soon as you get hit. Smite a Golem, then finish off the second one with AA.

Continue towards Wraiths and AA the Big Wraith following up with an immediate Alpha Strike. Activate Wuju Style and a Health Potion then continue to AA the Wraiths until they die.

Now head towards Wolves, repeating what you did at the Wraiths.

Head over to Blue Golem, use another Health Potion, AA the Blue Golem then Alpha Strike the mob. Activate Wuju Style and continue to AA the mob. Use Smite to finish off the Blue Golem.

Return to base

Head over to Red Lizard and repeat what you did at the Blue Golems. Finish off the Double Golems that spawned below. Pick a juicy lane to gank =]

Early 1-6:

Mid 7-13:

Late 14-18:

ALL SOON TO BE IMPLEMENTSEDEDSEDSEDSEDeD

ALPHA STRIKE TO VICTORY!

"A handy list for new players. Thanks to everyone in this thread for their contributions :) Feel free to reply to this thread with other terms and I or the mods will add them. Also report if any of the descriptions could be improved.

Ace: Finishing off the last person on the enemy team.
AD, Attack Damage: How much physical damage you deal with each attack.
Aggro, Aggression: This term is used to describe who, and how NPCs choose their targets. If you are being targetted by an NPC (tower, creep, boss) you have agro. There are various ways to break agro, such as moving into brush or getting out of the range of a tower.
AI, Artificial Intelligence: The logic that computer-controlled opponents will follow during a match.
AoE, Area of Effect: An ability that affects an area instead of a single target. This means anything standing within a certain distance of where the attack lands will be affected.
AP, Ability Power: A stat that increases the power of your abilities.
AP Ratio: The rate at which Ability Power boosts a champion's abilities. A 1.0 or 100% ratio means every 1 point of AP increases the power of an ability by 1.
AR, Armor: Decreases physical damage received.
ArP, Armor Penetration: Decreases the amount of physical damage your opponent's armor will absorb.
AS, Attack Speed: The time in between each of your attacks. DPS = Attack Damage / Attack Speed.
B: Short form that means different things depending on timing and context such as recall, come back, back up, be careful.
Backdoor: When one or more champions attack a tower without any minions to take the tower damage.
Bait, Baiting: Placing yourself in an open location, seemingly easy to kill, but you're just baiting them to your ganking party waiting in the brush.
BG, Bad Game: Used at the end of a match to express dissatisfaction with the results, usually because of people who have disconnected or left during the game.
Bot: An AI, computer-controlled character. More specifically, a character that is normally controlled by a human but is currently being controlled by a computer instead. Computer controlled champions are called bots, but creeps and towers are generally not called bots. A bot may also refer to a third-party program that takes control of the game to play for you, such as to cheat or gather experience and points while you are away from the computer. This breaks the terms of use for any online game and will often lead to a permanent account ban. It is also strongly frowned upon by any game's community.
Bot, Bottom: Bottom lane.
Brush: Brush is the tall grass scattered around the map that you can hide in. Players can use brush to break agro, escape, ambush, confuse, etc.
Buffed: A buff is a beneficial spell cast on yourself or a teammate that protects or enhances stats or abilities. This may also refer to the opposite of nerfed - when the developers change something in the game to make it stronger for the sake of balance, it was buffed.
Care: Means you have to be careful, they might be coming for you.
Carry: A champion that starts off weak but becomes very strong late game.
CC, Crowd Control: Any ability or action that can control an opponent, such as preventing them from moving or casting spells. Fear, Silence, Taunt, Stun, Slow, etc...
CDR, Cooldown Reduction: Reduces the cooldown of abilities, or the amount of time you must wait before an ability can be used again after you activated it.
Champ, Champion: The character you are controlling.
CrC, Critical Strike Chance: The percentage chance that your attack will be a critical strike.
CrD, Critical Strike Damage: The percentage of extra damage that your critical strikes will cause.
Creeps: The squads of weak NPCs that constantly spawn and fight in the lanes.
CS: Stands for "Creep Score", this is a common term used to refer to how many minions each player has killed.
D/C, Disconnect: Someone who disconnects from the game while it is still in progress.
Denying: Killing your own creeps just before the enemy player, denying them their gold.
Diving, Tower Diving: Running past an enemy tower in order to chase down an enemy champion, risking your own death.
DMP: Dance Master Phreak
DoT, Damage over Time: A term used to describe a spell that deals damage over the span of several seconds instead of instantly. An example is Malefic Visions.
DPS, Damage Per Second: A DPS champion is generally a term for a character that can do a lot of damage in a short period, whose gear and build is focused on dealing damage rather than support or defense.
ELO: A rating system named after Arpad ELO that determines how good you are relative to all the other registered players.
Facecheck: Sticking your face into some brush to check if anyone is hiding. Warning: may result in loss of face.
Farming: Killing minions repeatedly for money.
Farmed: Someone that has a high amount of minion kills giving them a lot of money to buy powerful gear with.
Fed: Someone that has a high number of kills giving them a lot of money to buy powerful gear with.
Feeding: Someone that is dying over and over to enemy players, feeding them free money. This is often an accusation, such as when a player wants to throw the match but his teammates do not, he may start feeding the opposing team. It may also be an insult, basically saying that the player has no skill and so keeps getting killed.
Gank: Gang kill or surprising an enemy for a kill.
GG, Good Game: Said near the end or after a match in good sportsmanship. If said while a match is still going, it may mean the player sees no way they can win and is admitting defeat.
Harassing: Using abilities and strategies that annoy and pester the enemy, slowly taking away their health and/or leading them to make poor strategic decisions. Taking pot shots from range repeatedly, for example.
HP, Hit Points: Your health, when your hit points reach 0 you die.
HP5, Health Regen: The amount of HP you regenerate over 5 seconds
IAS, Increased Attack Speed
Initiate: Used in reference to starting a fight or team fight. Who should attack first, or how. A champion, ability or strategy that is effective to open a team fight with, such as area crowd control abilities or tank built champions.
Juke, Juking: When you trick an enemy that's chasing you, such as using cover of bushes to make them go the wrong way and lose you.
Jungling/Jungle/Forest: Killing boss NPCs in the forest/jungle area.
Kiting: Dealing damage while keeping the pursuing enemy safely at range.
Lane: Maps are designed with corridors or lanes where the creeps and towers are.
Laning: Fighting in a lane, often used to indicate who you are laning with, or if you are solo laning.
Last Hit: To get the last hit on an enemy, getting the reward for yourself. Usually applied to minions.
leaver: Someone who leaves the game while it is still in progress.
Lom, Low on Mana: A warning to your teammates that you are almost out of mana and will not be able to assist or defend yourself much longer.
Metagame: What is currently "popular" in the game, what you are most likely to come up against in a typical game.
MIA, Missing in Action, Miss: When an enemy champion is not visible on the map, often a warning of incoming gank. TM/MM/BM may be used to indicate where an enemy player is missing, or where they may be expected to turn up (top/middle/bottom).
Mid, Middle: The middle lane on a map with 3 lanes.
MOBA: Multiplayer Online Battle Area, a term used to describe games like League of Legends.
MP, Mana Points: The blue bar below your health bar that most champions use as a resource to cast spells.
MP5, Mana Regen: The amount of mana you regenerate over 5 seconds
Mpen, Magic Penetration: How much magic resist your spells ignore.
MR, Magic Resist: Reduces the amount of magic damage you take
MS, Movement Speed: How quickly your champion moves
Nerfed: When the developers change something in the game to make it weaker for the sake of balance, it was nerfed.
Offtank: Usually the offtank is someone that acts as a backup tank in case the regular tank isn't around or gets killed. May also be referred to as "offensive tank", as in someone that can tank relatively well but still do a lot of damage.
OOM, Out of mana: You are no longer able to cast spells and are defenseless or unable to assist.
OP, Overpowered: Usually in reference to something that the player feels is unbalanced and needs to be fixed. A champion or item that they feel is too strong in relation to others.
Ping: Clicking the minimap to "ping" a location in order to get your teammates attention on that spot. Depending on the location and circumstances it could mean a MIA, incoming gank, tower about to fall, team fight breaking out, etc...
Pushing: Fighting in a lane with the intention of taking out enemy creeps and towers, to advance your attack.
QQ, qq: Whining like a baby. The Qs look like eyes with tears coming out in most fonts.
Re: An abbreviation for "returned", meaning that someone who was recently called MIA has returned to their lane.
River: River that cuts across the map. "Watch out for River, might be a ganking party there".
Scales: How a spell gets more damage based on your items - for example, Disintegrate scales with Ability Power because it gets stronger the more AP you get.
Scaling: Usually refers to runes, this means that it gets better as your champion gets to a higher level.
Sigil: Also known as "Golem" or "Lizard" buff.
Skill Shot: An attack that you have to aim.
SS: "Switching Sides", a common substitute for "MIA".
Starve: To prevent a player from getting kills through the use of harassment, ganks, wards, etc, starving them of gold and experience.
Tank: A champion built to absorb high amounts of damage. Tanks are the ones that should initiate team fights or pull aggro on boss NPCs.
Team Fight: Means exactly what it says. Late in the match teams will often travel in a pack and when they inevitably clash this is a team fight.
Top: The top lane of the map.
TP, Teleport: Teleport is a Summoner Spell that allows you to travel to any friendly unit on the map.
TT: Twisted Treeline, the 3v3 map.
Upper: Upper lane.
Zone, Zoning: Zones are areas of control, generally around players, NPCs and towers. Zones are affected by positioning, terrain, abilities, attack range and other game mechanics. Zoning is taking advantage of your knowledge and understanding of these zones to control the fight and harass/push/starve effectively while staying alive and safe."

Credit to Matt here on Mobafire for the keywords