Rend Blackhand 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 Rend Blackhand by first completing General Drakkisath.
Completing this Bounty will unlock the Razorgore Bounty.
Whenever an adjacent character takes damage, this Merc takes it instead.
Potential Rend Blackhand 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 Rend Blackhand Bounty: