Item build: Madreds + Boots (back at 800 gold) > Spirit Stone > Lantern > Phage > Trinity > build accordingly
My usual endgame turns out to be Feral Flare, Tabi, Trinity, Zephyr, Randuin's, and some 6th item that I'm not entirely sold on yet. Spirit Stone is what makes this build work imo. The sustain from the passive and additional monster damage means you can base far less compared to most other junglers while having the clear speed comparable to Yi and Rengar.
The pug Udyr I saw didn't go Zephyr but I think it's a very fitting item for Udyr with the AS/MS/Tenacity stats. Against champions like Viktor, who are getting more play time in pub games and have a very good CC ability, Zephyr becomes that much more appealing for melee champions like Udyr
Masteries are 21/0/9.
Skill order is QRRERWRER. After R is max, I tend to level W and E evenly. This might not be the most optimal and it's definitely not what Slayer suggests but I like having the utility from Turtle and Bear so I don't focus on straight max W second. By 18, I do max W and it depends if I need more DPS (Q) or MS (E) at the end game. Usually it leans towards Q max third.
I should preface this by saying that this is a very greedy build. You not only take 2nd Blue spawn for additional FF stacks but the CDR helps if you decide to solo Dragon which is entirely possible by level 7. You want to finish Flare by 15 min and it's not unusual for me to have more than 30 stacks before 30 minutes. Because your focus is far more invested on farming than ganking, you really need to be able to read the lanes and have an idea of where the enemy wards/jungler are. I tend to hardcore farm if I don't have Red buff but even then, there are times where you should go to a lane because you can get a turret a few minutes faster because of your DPS. As long as you stay on point with your farm, you'll go into mid game with 1-2 levels ahead of solo lanes perhaps and even 3-4 levels up on the enemy ADC.
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1557444160/28092?tab=builds
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1558508185/28092