Nefarian is an encounter inside the Blackrock Mountain set of Mercenary Bounties.
This bounty can be picked up from the Bounty Board and recommends a Party level of 30 to complete it.
You can unlock Nefarian by first completing Chromaggus .
Your characters cannot be Frozen.
Potential Nefarian Bounty Rewards
In addition to earning Mercenary Coins based on your Party members, Bounties are assigned to specific Mercenaries to allow you to target loot better.
The following Mercenaries can have their loot appear in the Nefarian Bounty: