[ NOTE : THIS BUILD, AND EVERYTHING FOUND IN THIS GUIDE IS EXTREMELY SITUATIONAL.
This is not a standard playstyle for this champion. If you are a rookie Udyr player,
I'd advise AGAINST IT. Also, avoid soloQ. This style requires a 3men premade at minimum. ]


Hello boys and girls, my name is PluckyPanda, an Udyr main player on the EUNE server, currently placed at gold 2(because of reasons).
I have been goofing around a while with different experimental builds on Udyr, and so far, this is the one which has the most carry power, in my opinion, of course.
With the recent changes to Enchantment: Runic Echoes and Udyr's Iron Mantle and Wingborne Storm, I have a feeling he will slowly be forced out of the current meta.

The build I will show you, however, might help you get to the exact opposite side of it all.
You might end up carrying games after games, ranks after ranks.

Summary

If you decide to use this build, you'll have one goal : To farm as much as possible as fast as possible, to have Enchantment: Devourer's Sated Devourer available very early. Keep in mind, that you won't be able to gank later on in the game. Your power lies in your waveclear, and 1on1 skirmishes.
You must take every objective you can. Towers, dragons, barons etc.
Your biggest threat is how fast you can destroy towers. You must take every opportunity to push a lane. You should always remember, that you're there to carry, not to play babysitter - never listen to your teammates whining. If you see the opportunity of taking a tower, go for it.

Early game

Your early game objective is to farm Enchantment: Devourer. Before you upgrade your Tracker's Knife to devourer, you should always look for early gank opportunities. Even if you only force a Flash or two, it was worth it. As soon as you buy Enchantment: Devourer, you must take an early dragon. Very important, that you should do it solo. Tell your teammates to ward and/or clear wards around drake. Note, that from this point on, you focus on farming. If you see a safe opportunity for a gank that seems like it could be successful, go for it.
In addition, both scuttlers must be your prey, at all times. This provides vision over river, also, makes flying around the map faster for you.

Mid game

Buying Guinsoo's Rageblade makes taking dragons a piece of cake, so make good use of that. You have to rush Titanic Hydra, faster than ever. After you got your so much anticipated power spike, the gates are finally open.
PUSH. EVERYWHERE. EVERYWHEN.
This is where you'll shine. If your team has the composition, and the players have the brains, you will be able to splitpush. Teamfights for you do not exist. They only serve as an indicator, that you're free to take a tower, or two. The enemy team will be forced to retreat and defend against you. You will always be lingering in their head, more often than not, one of them will recall to face you, meaning : You created a 4v4 fight opportunity for your team. Now, the choice is yours. You could retreat and push a different lane, or join the 4v4 fight, making it a 5v4. Either way, your team has the upper hand.

Late game

I mean, Udyr lategame. You're probably 18 now, almost full build, while the enemy team is still farming xp to get to lvl15. Two words. SOLO BARON.
Tell your teammates to keep the enemy team occupied, and away from top river - Also, remind them to play safe, don't force the fight.
If you reached this far, you're probably able to 1v1 literally anyone who gets in your way.

Frankly, I think I've covered everything an advanced Udyr player needs to be successful with this build, and in S6.
Hope you'll find my article useful, and thank you for reading.
I wish you the best of luck in the Fields of Justice!