You'd probably want to pick a ranged top or someone who could zone him effectively. I would bet Vlad would work well. He would sustain his once/6 sec harass of snowball pretty easily while simultaneously nuking Nunu every 5-9 sec and more with AAs. I wonder if you could pool under a snowball while it's in the air. Might end up costing you more hp to do that though.
You just farm... Youre not gonna kill him unless he messes up but he only has one thing to damage you. Hes cant even auto you since most top will destroy him if he walks next to them to fight. So just farm and take some pots... he cant burst you for a surprise kill so you have plenty of time to heal up. --- Taric is mai waifu
Chalice GP is pretty much guaranteed to win this matchup.
Anyone with an interrupt to stop his ult.
In fact I think Fiddle is probably one of the best heroes to go up vs Nunu - outsustain him, no way for him to stop or outdamage your drain, two interrupts. --- ~Victory needs no explanation; defeat allows none.~