There are no real counters to nunu, because he is about utility (amplifies his adc, does "good" ganks all game long, decent damage but low scaling, aura bearer, ...) he can go economic builds or a bit more expensive ones (abyssal let's say)
Now jungle-wise, nunu is both a farmer and an invader (at least it's his biggest strengths).
Thus you want champions that shouldn't be buried early game (amumu/hecarim for instance are not champions you should want)
On the contrary you want champions that are good gankers early, with maybe dashes/interrupts in their kits, while having a good first clear time.
Take lee-sin for instance. Nunu has a slow? So does he. Nunu has an execute (i mean, for objectives such as drake or nash), so does lee.
Now lee's R counters nunu's R "directly", and he has decent peeling power to stop a nunu that wants to throw a snow ball on your carry.
He also stops Nunu's good lategame, because he is a better ganker early, and thus you can snowball off of him your lanes before Nunu's Bloodboil starts making the ennemy adc a beast.
There are loads of champions to pick against Nunu, but long story short follow the guide lines :
- don't pick "weak" champions that have to farm untill six
- pick more according to your team and ennemies' teamcomp rather than simply against Nunu (he is just an amplifier with bullying power)
I might say stupid things tho.
Kool thanks, i dont actually play lee though lol. Most duelists cant catch the little bugger, he just ices you and scampers off.. but a few with gap closers and cc would be nice, maybe j4 or jax, but jax can get hurt badly without farm..