Bumba's Hammer will allow you to be constantly involved in team fights with the passive, as long as you are autoing in between your Thrown Axe, Bladed Arrows, and Hail of Arrows combo, this pretty much allows your Thrown Axe to be on a 1 second cooldown with max CDR.

Build Jotunn's Wrath before Transcendence, 20% CDR on a 2200 item with 45 power is insane, and can not be looked over. Ullr uses a ton of mana rotating with his 1 1 3 combo, if you find yourself not being able to conserve enough mana for your survivability, Transcendence first item will still work.

You will be over capped in CDR late game once you are full build, so now is probably a good time to sell Jotunn's Wrath for something else, like a Titan's Bane, Dominance, or maybe even a Bloodforge if you don't need the penetration. Or you can by some defense like a Magi's Cloak, or a Mantle of Discord, (you will be over capped in CDR again if you build Mantle but the defense is definitely worth it).