Glad it helped you. There's nothing to update, the build is the exact same as when I wrote it, in fact all the changes since then made my build better : for example huge Ultimate Hunter buffs, cinderhulk buffs, or the Aftershock nerfs which make Arcane Comet the better choice in an AP build.

Bad idea. Snowball Barrage already has a slow, and slows don't stack in league. Also, you can only throw snowballs for a total of 3 seconds with a 14 second cooldown, it's not like it's a permaslow or anything (unlike say Taliyah). Rylai is the weakest of the AP tank items, Nunu has far more synergy with morello (magic pen amplifies his huge base damage ratios), liandry (+10% damage on ult and lots of DoT), or protobelt.

Thanks, appreciate it. I haven't played the new Nunu in ARAM, I played the old one there a lot and he was really strong. It was basically Mark/Dash into teamfights and land good ultimates, or chesse people in bushes with ult. New Nunu is even better in that mode because he has his W to initiate fights on top of snowball, and even more sustain. As for item builds and runes, the build in this guide is fine. You can go Aftershock alternatively if you want to be tankier in teamfights.