Vaelastrasz 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 Vaelastrasz by first completing Razorgore.
Completing this Bounty will unlock the Chromaggus Bounty.
At the end of each turn, deal @ damage to all enemies.
Potential Vaelastrasz 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 Vaelastrasz Bounty: