Bogeymen are annoying and are the death of many low-level adventurers. They inevitably kill you until you reach a high enough level to fight them off reliably, and then they are simply a waste of time. Worst of all, you don't even get anything for fighting them.
What if that last bit was changed somehow?
The general idea is this: A custom creature called a 'soul wisp' may show up during a bogey attack. When killed, the wisp drops an edible 'soul'. Eating this soul gives you the power to 'face your fears', which can target only bogeymen and night creatures. It transforms regular generated bogeys (which I will call 'tier 0') into a random 'tier 1' custom bogeyman, which will be about as powerful as a regular (non-bogeyman) night creature. These stronger bogeymen, when killed, also drop souls. By eating a tier 1 soul, you gain the ability to transform tier 0 bogeymen into tier 2 bogeymen, and so on. These bogeymen could possibly be thematically based on common phobias: giant spiders, fire spirits, snakes, clowns (like, ACTUAL clowns)...
Eating bogeyman souls will sometimes (randomly) give you permanent powers thematically related to the bogeyman that dropped it. A fire spirit might let you throw fireballs, a bogeyspider might let you shoot webs, a bat bogey might let you turn into a bat man. Basically, it would be an alternate way of gaining special powers in adventure mode without having to storm a necro tower or get bitten by a werebeast, but of course you'd have to be strong enough to fight even stronger bogeymen, and you wouldn't be able to run away once you started...
There could also be a 'final boss' bogeyman (something even stronger than a demon) which, when defeated, would drop an extremely powerful item that could be used in fortress mode. Don't know what that item would be, though.
Anyway, I'm still working out the details... so does anyone have any ideas?
EDIT: Another idea - making each type of soul awaken only particular types of creatures. This would allow the adventurer to progress along a 'tech tree', similar to a class advancement system, but where the classes would be regulated by the types of bogeymen you chose to fight. Not sure if choosing one path should block off the other paths, though.