Sure the Dungeon Keeper games came with a manual that stated exactly which rooms you needed to get which creatures, but most creatures just made it obvious why they joined your dungeon. This provides a level of intuitiveness and atmosphere that is important. Some good examples of the Dungeon Keeper games:
- • Big fat bile demons are attracted by large hatcheries
• The dark mistress is dressed in an SM outfit and goes to the torture room for fun, and is attracted by the torture room
• Everything about the warlock says scholar, and he is indeed attracted by the library.
I would suggest to keep this in mind for Open Dungeons as well, and to link the attraction requirements to the look and personality of the creatures.
This is doubly important if you go for a tiered system where attraction of high tiered creatures is dependent on lower tiered creatures. Here you must have some sort of clear link between those creatures or otherwise a player will fail to understand how having more slimes will lead to having more trolls later on.