Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This is how I play Udyr, my way. Udyr, through my eyes is a well built champion, despite his nerf. In the hands of a good player, Udyr can be a indestructible force. Opposite for a bad player. You need precise timing on when do use Turtle stance, gotta know when to chase and flee. And knowing when to use phoenix. Having those advantages, makes Udyr a well built champion.
I like Udyr with some Armor penetration. So buy Armor Penetration runes. I wont show runes in the rune slot, but I will tell you a basic set up for runes. With the Red rune, I like to go armor pen. With the Yellow Rune, I like attacks speed and critical chance. For the Blue Rune, Critical Dmg, or chance is good. For the Quints, u want 1 Armor pen, 1 CD reduction, and 1 Atk speed.
For the Masteries, I choose mostly Defense for a reason. IMO Udyr is squishy early game, and i hate that. Also who doesn't want more dodge? If you dodge you gain 10% run speed.
I start off getting boots of speed, just because I like grabbing Berserker's fast. Get turtle stance and time it right. Don't trigger it right away, use the element of surprise. Once your level 2-4, if your team mate is good, go for a kill! You're almost guaranteed one with Bear Stance.
You start grabbing some kills in this part of the game. Your chasing skills you be outstandingly fast, and you'll rarely die with a combo of Bear and Turtle. If you have been fed, even 4 kills, 0 deaths. You can solo 2v1, and 2v3 for a short while. You just constantly switch between Turtle, Phoenix, Bear, Repeat.