So I tried Nunu recently... And I can see why he isn't played often
His Passive is Lissandra's only instead of a Timer it's after 5 auto's... It's not a bad passive, but there could be something better to fit him
His Q, yeah it buffs him, but you can't use it on Champs which is a tad annoying... Even if they changed the damage output so that it does the True damage to minions and some other amount of damage to champs would be nice
His W is similar to WW's plus a movement speed buff, but it kinda feels odd in his kit, like it was tagged on
His E, I personally felt it could use with a bit more range, and a bit more damage... But that's just me
His Ult... Really the only thing I can say the guy has going for him...
Sum it up... In the Jungle... He can take Objectives well and Farm the Jungle with Ease... But that's really it... Ganking feels a bit lack lustre on him since he really does need to rely on his teammate to make something happen with a slowed enemy and speed up movement, plus a Yeti punching the guy in the face...
His Kit mainly seems to be one that could be used to build him into a Support, with all the movement Buffs and Debuffs... But his win rate as support is abysmal
And you can only build him one way... A tank... There's AP scalings on him... But he can't damage champs with his Q, and his Ult has to cool down meaning he really only has access to his E to provide that extra punch
All in All... I think that Nunu needs a rework because he doesn't really have a lane or role that he can really latch onto... His kit is all over the place needing focus... and playing him doesn't feel fun or exciting or something else
And people can say that I'm wrong and I'm an idiot, and I could be, since I haven't played him much at all, but this is how I felt while and after playing him...
Just my Thoughts