The Dark Brotherhood skill-line is part of the "Guild" category in the Elder Scrolls Online. The Dark Brotherhood skill-line only has passive skills and the Blade of Woe, which works like a synergy. The Dark Brotherhood focuses on improving your assassin capabilities.
How do you unlock the Dark Brotherhood skill-line?
To unlock the Dark Brotherhood skill-line you have to join the Dark Brotherhood, which is only possible if you have access to the Dark Brotherhood DLC. To find the Dark Brotherhood you have to visit the Gold Coast zone.
How do you level up the Dark Brotherhood skill-line?
To level up the Dark Brotherhood skill-line in the Elder Scrolls Online you have to complete Dark Brotherhood related quests such as story quests, contracts or sacraments.
Call the weapon of the Dark Brotherhood to your hand and deliver a killing blow to an unsuspecting target. Experience from this target is reduced by 75%.
This ability does not work on players or difficult targets.