Pros-Good ganker
-Good jungler
-Very well at 1v1
-Has a single target stun
-Hard to chase/get away from
-A pretty tough champ
-Nice DoT with Tiger Stance
-Decent shield with Turtle Stance

Cons
-No Range
-CC can be a big problem for Udyr
-Big learning curve

Udyr can go a couple of different routes with items. I definetly like Trinity Force on udyr because it gives him plenty of damage while stance dancing. Trinity force plus udyr's tiger stance is your main source of damage. Udyr can go tanky if need be but i like going heavy dps. If you need magic resist i would suggest getting a catalyst to start then later making it in to Banshee's Veil. This item will not only make you tanky but also block the one spell per 30 sec. Obviously the first guide is if you get fed early game which should happen. If your not lucky and dont get fed then use the seocond build. Personally i like the second build better because it is more reliable and more realistic than the first. I have only gotten the first build a couple of times.

I like armor pen marks beacuse not only do they help early game, but they help late game. Some people prefer attack damage over armor pen but i personally like them better. The dodge seals beacause they synergize well with his passive. Now the magic resist glyphs are jus for those pesky caster that want to focus the hardcore AD carry. The quintessences are jus for early game survivability.