This is a jade druid list I came up with after struggling on this boss for weeks with different outdated netdecks. After throwing together some good cards I had, I was able to beat Nef down on my second game. The list is by no means optimized, I for instance don't have Aya Blackpaw or Fandral Staghelm which might boost the deck a little higher. 

Explaining card choices:

The deck is tuned to the fight, for instance with Biology Project for ramp as Nef already starts on 10 and Dragonslayer to get ahead on board against those pesky big dragons. Despite having Coldlight Oracle and Naturalize, this deck isn't aimed at going to fatigue, although if you get there you should win with auctioneer and shuffles. You want to stabilize and get ahead on board quickly by pumping those jades. To be able to play out, you want to mulligan for cheap jades and ramp, preferably Biology Project and Jade Blossom. Overflow is a one-off, simply because I only have one copy and I don't own UI - it treated me really well, as I was able to get in some jade value trades and heal them and myself up out of range to seal the board state. It is of course also an excellent draw tool. Kun the Forgotten King is not staple, but I still had it in my collection from Gadgetzan. With the refresh, it allows you to have a big tempo turn eg. ramp into Kun -> refresh -> Brann Bronzebeard + Jade Behemoth in the mid game allows you to start building a board that can trade favourably. I imagine Kel'Thuzad or another big boy might serve a similar function after trading your board away. 
 

Don't be afraid to use removal, as the deck's life gain isn't fantastic - rather get ahead and stay ahead. Nefarian has quite a bit of targeted burst that you would prefer to stay out of range of.