Hi! I am a Silver player on East Server with more than 100 ranked games on Udyr.

Reason I made this guide: I see a lot of people trying to mimic a certain playstyle of Udyr so I wanted to present a different one in which I am very confident.

Udyr is the only champion in the game which uses exclusively auto-attack as a source of damage, CC or sustain. He has no real abilities but just "Stances". Each one grants 2 effects:

1. Upon activation which lasts for 5 seconds (except E)
2. Permanently; until you change to a different stance

At first glance someone would naturally think:
"Wow, such a useless champion! You can't throw any skillshots, jump on someone or escape. He doesn't even have an ulti???"

That's partially true. Udyr though comes with some outstanding abilities from his stances and passive which make up for his lack of true abilities.

Let's start with summoner's spells!

VS VS

1. Arguably Flash can save a whole game if you use it to dodge a decisive enemy skillshot or make it alive out of a late-game teamfight. But... that's all! Udyr doesn't benefit from Flash until the very endgame. It's better not having that escape than sacrificing a potentially game-changing summoner's spell!

2. Ghost suits Udyr's kit (more speed is always welcome :D). It helps you kite, chase kill, escape by running between enemy turrets, gank and dive much better.
You should get this if you don't plan to upgrades your boots to homeguard early for whatever reason or if you want to have that un-planned chasing potential (please don't be confused about homeguards! just read No.3! ^^)

3. Teleport... the most OP summoner's spell (thanks to its synergy with homeguard)
So basically you want to upgrade your boots to homeguard ASAP!!! By that I mean after getting MadStone (yeah, even before completing Wriggle's). At early game use it to go back to your jungle faster and stack more. As soon as you see a gank opportunity, all you have to do it press "B", wait 7 seconds, then teleport to nearest ward and get the kill (or kills)!
You should teleport only after backing to get homeguard buff except in rare cases such as teleporting to escape or to split push super fast in the late game.

Level 1-3: Get your R first to clear the Blue camp fast. Then get your Q and add one more point to R to clear even faster. Your combo at level 2+ is Q-R-Q... repeatedly. Always start with Tiger and change ASAP to Phoenix to get that attack speed for more flame procs. When you change to Phoenix, wait for a second flame before going back to Tiger.

Level 4-5: You must take E at level 4 for the stun, it is essential to run faster along the map and it can help you chase a free kill. Grab another point to Phoenix if your don't need the lifesteal (you can delay W so much because of the Vampirism masteries).

After than max either E or W according to the situation and last Q.

Note this is just an example!!! Udyr is very flexible and you shouldn't hesitate to upgrade any stance according instinct. You can always mix it up!

Double-Edged Sword & Butcher: Essential for stacking as fast as possible.
Sorcery: More CDR = More EVERYTHING
Martial Mastery: Too strong to ignore
Fury (2/4): Decent Attack Speed. I get this because I don't need any mastery from other trees.

Tough Skin: Provides you with early resistance against jungle creeps.
Bladed Armor: Helps clearing the jungle faster.
Enchanted Armor: Gives about 8 Armor and 5 Magic Resist at full build. I get this just to be able to grab Bladed Armor.

Fleet of Foot: Movement Speed is important on every jungler, especially feral stackers.
Runic Affinity: Udyr benefits from both buffs very much, blue is crucial before getting mana items.
Alchemist & Culinary Master: Nice for sustaining jungle early on.
Vampirism: 3% Lifesteal and Spellvamp is too OP I think. You proc Spellvamp from Phoenix's flame waves and Tiger Strike.
Phasewalker & Summoner's Insight Absolutely insane combo for homeguard TP ganks. Also you have smite 4 seconds more frequently.

These are the ideal boots to get. If enemy team has too much CC, magic damage or heavy Auto-attackers you are better off picking Mercury's Treads or Ninja Tabi respectively. This is your carry-item.

This is the core item. It upgrades Udyr's kit to a brand new level: Q is boosted by AD & AS W is boosted by AP & Health E is boosted by MS R is boosted by AP The extra mana is very nice and Critical is fine as it scales with AS which means you will pull some crits off even with 10% chance.

CDR lets you use your stances more often which translates into more damage and lifesteal, as well as extra movement speed from Udyr's passive. The Mana it provides waves you not to worry about spamming stances. The passive of this item along with the Armor turns you into a anti-carry champion who can 1v1 any auto-attacker such as ADCs and Assasins like Fiora.

Pros

+ Safe pick + Insane map control + Legendary split pusher + Tanky Nature + Highest AS & MS steroids + Spammable Stun + Strong counter-ganking + Good duelist + Level 6 solo Dragon + Great Teamfighter + Hard to kite + Hybrid Damage + AOE Damage + Infinite stacking

Pros

- Can only auto-attack - Mana hungry early on - Jungle-farm dependant