The Raiders are the lightning quick version of the regular mounted units (i.e. cavalry). The guerrilla warfare tactics practiced by the Rangers were limited to ambushes, so the Raiders extended this deadly repertoire by adding a hit-and-run element. They are usually the first to engage the enemy army and slow it down with frenzied attacks.
To keep the enemy occupied in between assaults, they coat their weapons with various poisons. Even a small scratch can leave a soldier merely limping along the main column.
The Raider's main objective is to destroy the enemy's will to fight and nothing hits morale harder than seeing your commanders fall. That's why a few elite Raiders have focused exclusively on infiltration and assassination of key personnel. They have traded their mounts for stealth.
Often, an enemy commander hit by a poisoned Raider weapon will be finished off while recuperating in his tent by one of these elite Assassins.