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.
Udyr can be built any number of ways. The best way to build him is to buy items that give him survivability and attack damage. Ninja Tabi are good because he dodges attack and it gives him armor. The Brutalizer gives him a little extra to his hits early game. Frozen Mallet gives him health and attack damage. It also keeps the enemy within striking distance with its slowing effects. Force of Nature is going to add to his already large amount of mana regeneration being received from Turtle Stance. It also gives him much needed Magic Resistance. Starks Fervor benefits your whole team and also gives Udyr more life steal and survivability while also allowing him to attack faster. Phantom Dancer makes Udyr faster in all aspects of the game and at this point catching, tanking, and killing should be easy.