From Lexicanum

This article is a stub

The Scythians are a race of little known alien warrior-monks, who were first encountered by the Crimson Fists sometime after the Horus Heresy, during the cleansing of their home system. Very little is known about them, except that they came from a region of space designated HR8518. During the crusade they specialised in underhanded surprise tactics, and preferred the use of venom-based weaponry, such as their much-feared Scythian Venom Talon. During the war they met with only limited success, but were able to strike down the first Chapter Master of the Crimson Fists. Some were able to survive the genocide, and the race lives on as mercenaries, often offering services as assassins. Like the Tarellians, they are always keen to exact revenge against the hated Imperium.

Sources

UK WD288/ US WD287 - Index Astartes, Bloodied Fist - the Crimson Fists