The Shadowscales are a special part of the Dark Brotherhood. In the Argonian homeland of Black Marsh, those born under the sign of the Shadow are taken at birth and presented to the King of Black Marsh. A Shadowscale hatchling is then trained in the arts of stealth and assassination by the Dark Brotherhood, and lives a life in service to the mighty kingdom of Argonia. Any Shadowscale who lives to come of age is accepted into the Dark Brotherhood as a full member of the family.
Shadowscales probably follow the same five tenets traditionally followed by members of the Brotherhood. However, the only ones that are known to be true are, never disobey or refuse to carry out an order from a superior and never kill a fellow Shadowscale. The only difference between these is that, if a member of the Dark Brotherhood kills a fellow family member he must fight the Wrath of Sithis to earn forgiveness. With Shadowscales, however, refusing to fulfill a contract is viewed as treason, and the traitor will be put to death. With the death of the last known living Shadowscale, it is possible that the Shadowscales have been entirely wiped out.