When I declare war, very infrequently the defender will raise an army that has the appearance of a knight on a horse checkered black and white (normally armies look like infantry in my game). It has very weird/broken behavior:
- It may or may not acctually attempt to fight in the war. Sometimes it will stay in the county it was raised, sometimes it tries to participate in the war.
- If it does try to fight me, it instantly loses with no casualties and no morale loss.
- If it tries to siege, it will be unable to (insufficient numbers).
- If it joins up with another army on its side, the buggy unit is kept, but if it tries to siege or fight, it will have the numbers of the army it absorbed (but still none for the original army).
- It still contributes to its owner manpower total in their character view.
My only guess is that it's a holy order, but I've seen ones much larger than any holy order I could hire.
EDIT: Just to describe how buggy they are, since I didn't take any pictures, this can happen:
The ghost army is trying to siege (and not doing anything) one of my counties.
I move my army to that county. The battle instantly ends, with 0 casaulties for either side. The ghost army, still at full morale unlike a defeated army, flees to another county.
Now this is where it gets super buggy:
The ghost army still wants to take my county so it will immediately return to the county it just fled from. As soon as it arrives, it instantly loses and flees again.
Then the whole process repeats. During one war, I left an army on one of my counties, and it defeated the same ghost army 30 - 40 times during the course of the war because the ghost army would just flee and return repeatedly.