This Guide is for a very aggressive and also durable Tiger Udyr build. You will be a very strong 1v1 dueler, very fast and sticky as well. You will be running,shielding and dueling a lot with this build. This champion is recommended only to players with good dodging skills since Udyr has no dash,leap,jumps and can only run to dodge skillshots or reach his targets.
Be sure to check some of my other guides if you like this one:
Reworked Jungle Swain
Unstoppable Warwick
Shadow Assassin Kayn
In-depth Kai'sa guide
Reworked Jungle Irelia
Jhinsoo Wonder Guide

Bridge Between(Passive): Udyr has 4 stances(his 4 abilities) which interact with this passive. When Udyr switches stances(casts an ability), his passive grants him 10% attack speed and 5 movement speed which stack 3 times and last for 5 seconds. You can keep this going for as long as you have mana if needed.

Wilding Claw(Q) : This stance gives you a bonus of 30-70% bonus attack speed for 5 seconds (rank 1-5) and also applies an on-hit effect on every 3rd basic attack which does damage over 2 seconds.(We're going to be maxing this first as our primary source of damage).
Iron Mantle (W): This stance gives you a nice shield which starts with a base of 60hp and goes up to 200 + gets a 50% bonus from the AP that you build and every 3rd basic attack heals you for 2.5% of your maximum HP,this heal goes up to 5% based on your missing health.(this is why we max this second)

Blazing Stampede(E): This stance gives Udyr a nice needed movement speed boost and allows him to ignore unit collision.This stance also makes Udyr somewhat of a CC train as it allows him to stun champions on his first basic attack for 1 second; it does however have a 6 second cooldown per champion stunned.(it also has a mini-dash towards the champion you hit; we're taking this as our third ability for better speed and dodge ability)

Wingborne Storm(R): We're taking a point in this stance in the midgame due to the area of effect damage it adds (in a cone in front of Udyr and around him as a burning effect like the sunfire cape) every 3rd basic attack.(we're getting the last 3 points for this in lategame since we don't really need more than 1 point for midgame with this build)
Note: Every stance allows you to use it's effects on THE FIRST HIT and then on every 3rd attacks(the only exception is bear stance which has the 6s cooldown per champion mechanic).

We're going to be taking the Inspiration and Sorcery Rune Paths for this build as they are the best for this type of Udyr in my opinion.
As our Keystone rune we have the Glacial Augment which allows us to slow our targets with our basic attacks, this is extremely good for Udyr as he has a lot of movement speed in his kit and has no leaps,jumps or dashes.
Next we have Magical Footwear which is by far the best second choice ,for Udyr, out of the current 3 runes due to the recent Inspiration path nerfs done by Riot.
In our 3rd slot we have Future's Market which is really a no-contest rune in that slot. It allows us to get our midgame faster which is what we want with Udyr.
The last one is Cosmic Insight which gives us some nice cooldown boosts for Udyr so you can cycle between the stances faster, this makes Udyr even stronger since we can get more procs out of our stances faster.

Our second path is the Sorcery and the first rune is Celerity which gives us a nice 1% bonus movement speed and an extrmeley decent boost to our AD based off of the movement speed we have as Udyr's Blazing Stampede increases our movement speed by quite a bit.
The last rune we're going to be talking about in this guide is Scorch, now this is extremely good with this build since Udyr already has a damage over time ability in the form of his Tiger Stance(Q), this adds another damage over time effect on top of that which only makes Udyr stronger in dueling other champions.This effect has a 20s cooldown which is a lot but you really only need one proc of it to count.

For the Press the Attack build we're going with the same setup I have in my
Warwick guide, for those who haven't seen it yet, you might want to check it out at the following link -> Unstoppable Warwick Guide


Press the Attack works great with Wilding Claw Udyr , it boosts your damage nicely.
Triumph is great in general for carrying the game as it gives gold on takedowns.
Legend: Alacrity this rune boosts our attack speed and it's great on Udyr because of the synergy with our passive Bridge Between and Wilding Claw which also increase attack speed.
Coup de Grace gives us a decent damage boost on low HP targets which we want.
For the second path we have Celerity with Waterwalking both increase movement speed and damage, both standard runes for river and map control but also for fighting in and out of river. The alternatives for Waterwalking are Nullifying Orb which gives us a Hexdrinker-like shield and Scorch which increases our damage over time further and has great synergy with Wilding Claw. We're one aggressive jungler so don't be afraid to show it.
Phase Rush is also an extremely good alternative as we can get out 3 basic attacks pretty fast as Udyr and it works extremely well with Celerity in boosting our AD.

You start the jungle at your Blue buff, ( do not smite as this is needed for stealing enemy Red buff) right after you finish you rush at the enemy Red buff which should be around the time the enemy jungler reaches this side of the map; you now have two options: 1.wait in the bushes next to the Red buff camp and kill both the enemy jungler and the Red buff or 2.rush the Red buff down,smite it, pop the red plant for a safe and quick escape over the wall into the Dragon Pit.
The next thing you should be doing is clearing the Rift Scuttle and backing, doing a full clear of your own jungle then gank or gank right after you kill the Rift Scuttle.
You should be looking to gank a lot as this build allows you to stick to your targets after level 3 with ease, hence why we took the Glacial Augment keystone rune which allows us to not only slow the target but stay extremely close and secure kills due to Bear Stance's stun.

Pros
- really strong early-mid game
- really fast movement speed so you can dodge abilities and/or flank
- added slow effect on basic attacks for even better dueling potential or teamfight presence
- durable with high damage output
- has an onhit stun with a 6s cooldown on the same champion
- the one and only jungler that can duel with warwick and possibly win
Cons
- has no dashes,leaps or jumps
- has to get movement speed in order to reach targets and secure kills if a lot of CC is involved
- has to get defensive items so he doesn't get killed while being kited around
- Trinity Force is a must for the added cooldowns,mana,movement speed,damage and survivability early-mid game(this isn't necessarily a con but i think being forced to buy an item is)

Update 1 patch 8.7 (4/4/2018)
- Added secondary rune path
- Added secondary item build to match the new pathing
- updated Runes section
Update 2 patch 8.14 (26/07/2018)
- Updated guide to patch 8.14 ; a lot of things have changed for Udyr and he got better overall in the last 2-3 patches