The Shadowscales are an order of Argonian assassins originating in Black Marsh. Argonians born under the sign of the Shadow are taken at birth and offered to the Dark Brotherhood, where they are trained in the arts of stealth and assassination. Shadowscales can recognize other members of the order by unique medallions. They are typically brass and inscribed with the likeness of Sithis, the Dread Father. Any Shadowscale who lives to come of age is admitted into the Dark Brotherhood as a full member of the family. They may also renounce the Brotherhood to serve the Argonian people in Black Marsh. They act with immunity there; some are said to serve as personal assassins to a King of Black Marsh. However, no such king is believed to have ruled since the height of Argonian civilization in ages past—if at all—and the sovereign's role as leader of the Shadowscales is exaggerated.

Shadowscales obey the same five tenets traditionally observed by members of the Brotherhood, although they are a distinct set of rules. For example, a Shadowscale cannot kill a fellow Shadowscale even if they are not members of the Brotherhood. However, breaking a tenet of the Brotherhood invokes the Wrath of Sithis, and forgiveness is achievable if the family member survives the encounter. If a Shadowscale breaks a tenet, it is viewed as treason, and the perpetrator will be put to death. This is usually carried out by the Argonian Royal Court, who will send an unaffiliated assassin to carry out the execution. During contracts, Shadowscales seek to kill their targets swiftly. Lengthy and brutal kills are generally frowned upon.

Shadowscales are reptilian kith born under the sign of the Shadow. Plucked at birth and offered to the detestable Dark Brotherhood, these hatchlings are a boon to their cause and are expertly trained in the arts of furtiveness and subtle bloodshed. When fully formed, they are embraced by these Sithis cultists and accept warrants for assassinations, just as their higher race kin have infamously done. Now that Shadowscales are incorporated into Argonian society, their targets benefit only the lizard-folk. How such targets are determined is still unclear.

It is believed the Shadowscales follow the identical five tenets of the hated Brotherhood. Through capture and torture of suspected members, we know that an order is never disobeyed or refused if given by a superior. A fellow Shadowscale is never a target of these cutthroats, and Shadowscales deserting the Brotherhood are hunted and slain. As our dealings with the Morag Tong have taught us, an assassin's guild functioning as an adjunct to an official government is a powerful threat: now the Argonians have organized such a force, which must be watched, infiltrated, and utterly confounded until broken.

I have gathered the following "Prayer for a Shadowscale" from a contributor who wishes to remain unnamed. My investigations have made me convinced that this is legitimate.

Hail to Sithis, the ever-changing.
What is consumed is restored.
The nothing of the Void, the whisper of the Hist.
Blood whetted blade, you have watered the roots.
Pass through Shadow and return.

It seems that most, if not all, Shadowscales in the years 582 to 586 of the Second Era were against the formation of the Ebonheart Pact. As a result, many left the region or fought any Pact troops that entered their borders.