In the PBE, his R's cooldown and mana cost are lower.
With max CDR, his ultimate will be usable every 1.2 seconds and cost 800 mana at max stacks.
Here's the build.
.
Last item can be 
, whatever suits your fancy.
But basically we're doing CDR Mana-beast with this guy now
PyramidSwim1 votesBuild path is awful, though, you won't contribute anything in the mid game stacking two tears and a rod. You'll just be hoping your team does well enough for you to make it to late game.
Crett1 votesI think you meant
and not
Also without the chalice you would only have 35% cdr with masteries. Switch Iceborn to Lich Bane since it would work well with the AP from Seraph's Embrace and is in general good if you are using abilities every 1.2 seconds and then get Chalice last no matter what for the 40% cdr and don't bother with cdr masteries since you will get 40% anyway and instead you could get some thing like maybe even attack speed.
I took iceborn gauntlet specifically over lich bane, not just because of the added mana, but for the tankiness, cdr, and most of all the spammable aoe slow. I was able to catch people out from so far away for my team just because of the slow. My mobility started meaning something for the rest of my team that way, and it was pretty awesome.
The build gets a LOT of damage from the mana, considering you can use it every 1.2 seconds (with chalice) Ult was taking people out pretty fast (the rammus wasn't building MR. woe is him.)
I only regret it doesn't smoothly reach 40% CDR this way. 10% is wasted.
Build path is awful, though, you won't contribute anything in the mid game stacking two tears and a rod. You'll just be hoping your team does well enough for you to make it to late game.
It's true. It's a late game build. You end up pretty beefy at the end, though, and R does 600+ damage.
Juggernaut6281 votesIn the PBE, his R's cooldown and mana cost are lower. With max CDR, his ultimate will be usable every 1.2 seconds and cost 800 mana at max stacks. Here's the build.
Last item can be
I think you meant and not
Also without the chalice you would only have 35% cdr with masteries. Switch Iceborn to Lich Bane since it would work well with the AP from Seraph's Embrace and is in general good if you are using abilities every 1.2 seconds and then get Chalice last no matter what for the 40% cdr and don't bother with cdr masteries since you will get 40% anyway and instead you could get some thing like maybe even attack speed.