My idea is that when a particular ghost is captured, a special ghost hostile to the ghost will appear.
Well it can be achieved but you will need to play with custom npc's as well. I will need to edit the code a bit but here's what you will be able to do if make changes.
- Long tongued ghost NPC spawns at random location in the map if she is captured. She will tell you about ghost room and current location of coward ghost. I edit custom npc thing so they can follow player around but it's a lot of work so I will leave it as is for now.
- As for Coward ghost. She will spawn at random location in the map when captured. When ghost hunt has begun she will spawn flame at player location that will lead to a hiding spot.