Ok so the spectral wraith pick up is the furthest from meta item in this build on Udyr so Ill cover that first. The reason I buy it is how incredibly cost effective it is. Not only do you get the 40 Ability power up front but a bonus 1 AP for each monster you kill in the jungle (Up to 30 ). Thats 70 AP and its incredibly cheap if your clearing quickly which because your playing udyr and maxing out the R you will be. You also have the 10% Cool down reduction which is also great and finished with the new massive sustain off of your AOE allowing you to easily donate blue to your mid laner if needed.

Ok so the other core item I suggested was Spirit Visage and Ill cover that as well. This item is also really cost effective on udyr. You double the sustain from wraith and add another 10% cooldown reduction plus the HP and the magic resist. You will have unlimited spam on your skills to be incredibly mobile with your passive and clear faster then most junglers plus if they have lots of ap all the better. The Mobility boots is a simple pick up just more mobility really.

OK lets talk different scenarios. If they have lots of AD randuins is your best bet because it also improves your ability to meat shield for carrys with the up front stats plus the slow. If you get fed buy Zephyr or tear stack that tear in 12 seconds due to your udyr spam and then manamura for raw damage and single target rape. If your behind Warmogs, sunfire, is the best choice and then finish with maybe a Atma or even a rylais if your feeling creative

This build works best as a hyper farm up your items then split push the **** out of a lane and force people to try and kill you when you know it takes forever and your team mates push other lanes, objectives or team fight. Your phoenix will do about 200 dmg every 3 auto attacks and 50 per wave so take advantage and clear waves uber fast for your pushing fun times.

Ghost for more mobility and smite for your jungling. Simple ****.