They were a force of warriors in full plate armor and closed helms bearing lances and mounted upon horses. They appeared and sounded completely solid and real. When manifested, they rode their mounts at a gallop through the full length of the pass, with lances lowered. They turned their helms to face any living beings they passed on the way, but passed straight through anyone or anything in their path, whether they attempted to bar them or were unable to get out of the way.
However, their touch caused no damage, instead only applying a fleeting chill and a brief pale blue glow similar to the faerie fire spell. It also caused all magical dweomers to produce a flickering ruby-red glow. This could reveal magic items lost by the road or on travelers slain by local orcs, or expose hidden or disguised magic on others.