This is an Udyr jungle guide with the build and masteries that I use. I'll keep pdating the guide when I have an idea for another trick that helps you.
This is my very first guide, so if you think something is wrong/not well-explained, leave a comment about it and how would you change it, and I'll update the problem as soon as I can. I'm in my 1st year of high school, so I'll have to study a lot. This means that I won't be able to look at my guide(s) very often. With this build, I got a pentakill, so it is possible to be good (or god?) with the final build example or other combinations of those items. So let's get started!

[*] Fast clear potential [*] Not expendable
[*] Can turn into hypercarry [*] Won't work instantly vs noobchamps
[*] Udyr
[*] Can help allies to get fed



//there will be more from both, I just have to think more about it ;)

I'm currently trying to finish my rune page for AD champs, so I didn't represent any here.
//I use the AP runes I use for Heimerdinger, so it is very interesting ;)

My choice of summoner spells are smite and ghost. Sometimes I change ghost to flash, but ghost is more expendable than flash. When you have to hurry to a team fight, or stealing drake/Nash, then ghost would give you the proper movement speed boost, e also gives you bonus speed, so e+ghost from base, or from far points. The well-known rule is that "You cannot outrun Udyr.", so you can use ghost when you have to flee because of low health or low mana, and you can't recall safely.

Skills:

Tiger Stance(q): this skill gives you attack speed for a limited time, and the special of tiger stance(). Use this before using r or w, because the attack speed won't be lost from activating another skill.

Turtle Stance(w): this one gives you a temporary shield and the unique of turtle stance(lifesteal). Use this to keep your passive alive, and when clearing jungle early and mid game.

Bear Stance(e): your second important skill. It gives you temporary movement speed, and when you hit an enemy/monster/minion, the victim gets stunned, then you can use your ult.

Phoenix Stance(r): your most important skill. You'll blow flames on activation, and after 3 hits. The flame damages everything it hits behind your enemy(and the target of course).
Use on enemies after e, and for faster killing, use q+r if the enemy can't go away.

So when the game starts, you buy your first items. I prefer going to the gromp, because after that there is the blue so close, and the buff will be enough for the first clear. When moving to the blue, ask your mid laner or someone who is not close to the gromp to put a ward to the red right after minions spawn. If enemy is there, then try grouping up, because your first clear is important to be fast. So send your allies away when the gromp has half of his health, ult again, and when you are alone, smite him. Then you go for the blue, w+r combo repeatedly, if you are at 50% health, then use the first health potion. Then proceed to the wolf camp. Use q+r--> w+r combo. Then you should go to the phoenix camp(I'll call them chicken from now). Keep your smite for the red, it gives you bonus hp. Then the last camp, the krugs. Now you should have above 800 gold, and level 4, so all your skills. Now you can recall, buy stalker's blade and boots of speed. Take a look at your map. By the way, it is important to ask your teammates to play safe until you can gank(or it is "highly recommended), as it will be hard to take down fed enemies. So you'll see how your bot lane is. If they are in a pushed position, then ask them to fall back, let the enemies come. Udyr's early ganking key is in the backstab, so coming from behind. You arrive to the proper bush(see in ganking chapter), target the enemy adc, activate e, ghost, if the enemy tries to leave. stun adc, then r, and q(r deals a good amount of damage, so thats why you need it), and if your adc and support helps you well, then you're gonna secure a kill. It does not matter if you get the kill, or your adc does.
When done, and you have enough hp, then you can return to the gromp-->blue-->wolf-->chicken-->red-->krugs jungling route. Meanwhile you are trying to get the 1400 gold for the cinderhulk upgrade.
Around level 8(6-8), you should go to take the dragon. if you go solo, then get a blue or 3 mana potions, and start with rift scuttler. If you have the required mana regen stuff, then you can start with a gank on bot lane, and get at least one kill for your team, and if you can, force a summoner spell out from the other, or-even better-, go for a double kill.
Then you can go for the dragon(kill her using your smite, never smite earlier).

At first, let's have a look at the buffs you can get from smiting the monsters in the jungle.

Gromp: The smite bonus gives you a passive ability: when an enemy/monster attacks you, they get poisoned, and take magic damage. I don't think it can save you, but it gives a slightly faster clearing potential and tower saving.

Wolf: A ward flies to the bush near the blue. when an enemy steps into this part of the jungle, the ward shows an "on my way" ping on minimap, and goes to the location. If the enemy is still there, then comes an "asking for assistance" ping again on the minimap, and the enemy is visible from now until he goes away from there. This can be useful when someone tries to take your jungle, but not that effective(it can save the day).

Chicken: Smiting her gives a buff that allows you to gain true sight when an enemy ward spots you. This is very helpful when preparing a baron takedown, or a gank, or just roaming in jungle(enemy or ally).

Krug King: smiting him will allow you to stun your opponent after every 6 auto attacks. This is useful when you want to ensure the success of your ganks.

blue and red: smiting the blue restores a nice amount of mana, the same with red, but it restores your health. when fleeing, and close to an alive red camp, you can smite him to have bonus help(I could never use this because late game red is almost always taken :( ).

For now, we can discuss ganking tactics and the proper method.
When the lane's situation is ideal(so the enemy pushed your ally/allies to the tower), then you can use ghost, if you want to be there fast, I usually use e 2-3 times, if it eats my mana. Otherwise I use e a few more times. approach the bush you'll go from.
On top lane, in blue team, use the tribush, in red team, go under the krugs camp, through tribush, and come from the river.
On mid lane, you can come from the side, or from the stone walls next to the river.
On bot lane, in blue team, go from river-, in red team, go from tribush.
While hiding and preparing, activate w to start the passive stack, target the enemy who you will stun, e, run, stun(hey that rhymes!), r, then start q+r->w+r combo(stun again if you need to, but note that you can't stun the same enemy for a couple of seconds). If the enemy dies/uses a summoner spell, that is a success.
If you see the enemy's jungler ganking, then you can put an alert ping, but if you can, then go into their jungle and steal camps. Stealing dragon or baron is a bit harder, as you have to be ready to use smite, but enemy team's skills, jungler's smite, and critical hits can screw it up, so be ready to be part of the "blame everything on the jungler" stuff. This is normal until you find a nice team, who played safe till they got fed, and would not blame you if you make any mistake.

In late game, you should have 4 items. Stalker's blade, mercury's treads, trinity force, and zephyr. Now your core item could be bloothirster. This one with zephyr, is a perfect item combo, but you probably won't be able to 1v5 the enemy team and survive(if they are feeders but don't have enough kills, it's easier to get them). So now you have a great clearing potential and life steal. You should get chicken's smite bonus, when the team goes for drake, Nash, or push to victory. You should run around the pit of the monster you want to slay, then take out enemy wards and let the fun begin. Always call the top laner(tank) of your team, then go for the enemy, but be sure that other teammates are actively battling and aren't letting you down. With proper teamwork, victory can be easily taken.

I hope this guide helps for you to become a good Udyr jungler. If you have any further questions, then ask them in a comment, I'll try to answer as soon as I can.
//Now comes the begging time
If you liked this guide and it was helpful please vote it positively, so I know that I'm on the right path. Good luck and have fun.
P.S.: Take them down, and don't let yourself to be blamed :) .