Mad Bomber Heroic is an encounter inside the The Barrens set of Mercenary Bounties.
This bounty can be picked up from the Bounty Board and recommends a Party level of 20 to complete it.
You can unlock Mad Bomber Heroic by first completing Barak Kodobane.
Potential Mad Bomber Heroic 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 Mad Bomber Heroic Bounty: