In Overlord there are 3 types of Ruborian raiders,They originate from Ruboria.
Castle Spree Raiders
These bandits have a suit which is very light grey. Unlike the Ruborian Raiders, these ones do not throw spearing darts at you. They can hit you with a lot of damage at a normal strike rate.
Slowly guide the Raiders out of the entrance of castle spree then put some reds behind them (Far not to far away enough so they can target the Raiders carefully and they have to be on a guard marker.) Then you have to keep the raider following you in a loop but not outside the reds firing range and your result should be successful.
Note: They do not appear in the arenas possibly because they look too similar to a Ruborian Fighter and because their attacks are slow and they don't do that much damage.
This type will appear in the following: Evernight temple, the Ruborian Dessert, Save Spree!, and Khan's boss fight. They do an ideal amount of damage for your current level of armour and minions but they can kill reds, greens and blues very easily with just one dart shot.
They have a dark grey and a dark purple coloured suite, They have a dart shot ability that can only be used once and they have a fast melee hitting speed.
When you go near a this type you must keep moving in random directions to make it less likely to get hit by their darts. Next you must send in 3-5 browns to hold the enemies ground and then you sneak behind with 8 greens and you send them on the back of the Ruborian Fighter.
This type have a very red suite and they hold a magma ball. They will appear in the following: Ruborian Dessert, Save Spree and Khan's boss fight. they have an infinite amount of fire bolts that they can throw at you. they can take out a pack of your browns with full armour within 3 shots.
When you have to face this type, you will need to use the slow spell when you have 12 greens and 3 browns. When you have the following you must then turn your slow spell on and send in some browns and sneak behind this enemy and send in the 12 greens.
Note: They appear to be called the "red flamed bandits" in Overlord Dark Legend.