Scythian Horse Archers rely on their mobility and missiles to weaken their foes whilst remaining out of harm's way themselves. Eventually, exhaustion, casualties and disorder will lead to the enemy's rout.
Scythian Horse Archers are not different to their many counterparts in their approach to battle. Only lightly protected and often with little more than a short sword as melee weapon, they rely instead in the power of their excellent composite bows and the speed and endurance of their sturdy steppe horses (and possibly the use of remounts). With these tools, they torment foes that cannot catch them or shoot back (or are outranged) with arrows until mounting casualties, exhaustion, sheer frustration and, perhaps, a rightly-timed charge by the core of heavier cavalry that often accompanies the horse archers, bring about the collapse of the enemy. Then, they will be eager to join in the pursuit and, thanks again to the speed of their mounts, they will be ruthlessly efficient in this task as well. Routing foes pursued by them have only very slim chances of escaping. As a part of a combined-arms army, they can harass an enemy, disrupt its formations and, with feigned flights, lure their troops to cunning ambushes. A judicious commander will seek to benefit from the strengths of Scythian Horse Archers and to minimize their weaknesses by deploying them in loose formations, in terrain that does not hamper their movement and by wisely keeping them out of hand-to-hand combat until the time is right.
Historically, the Scythians were largely responsible of first impressing on the minds of the settled peoples the image of the wild, steppe horse archer visiting destruction upon civilization. To some extent, they were preceded in this by the Cimmerians, but the extent and consequences of the Cimmerian invasions, large as they were, did not reach the scale of widespread devastation associated with the Scythians. In the 7th century BC after having subdued Media for some time and having contributed to the definitive fall of the Assyrian Empire, the Scythians poured over Mesopotamia, Western Asia Minor and the Near East ravaging and plundering as they went. Before crossing back the Caucasus and returning to the steppes, they would reach the very doors of Egypt, where Pharaoh Psammetichos paid a heavy tribute to see them depart. They wreaked major havoc that has left a diversity of lasting memories. The texts of the prophet Jeremiah in the Bible, the many Scythian trilobate arrowheads of cast bronze stuck in the brick walls of burnt cities over a very wide area, the writings of Herodotus or the city named Scythopolis (modern Beth-Shean in Israel) are some of the most conspicuous ones. Later, in the 6th century BC, Darius I, Great King of the Achaemenid Persian Empire, would claim retribution from past wrongs as the reason for his invasion of Scythian lands in the northern Black Sea coast. The invasion ended up in failure. Herodotos' account of that campaign is a textbook example (possibly the first recorded instance) of the application of the strategic retreat and scorched earth tactics and of the difficulties and dangers associated to fighting steppe nomads in their home turf.
These men are good horse archers and that is their only role, besides killing routers. They are able to rain arrows upon their enemies, and they are able to use the cantabrian circle formation to battle archers and other horse archers. Aside from that, they are poor melee attacks and should either leave the combat to infantry or other powerful cavalry or retreat.
They are very useful for any faction, especially those without any dedicated horse archers as they can be recruited by everyone.