I wanted to do something so that certain conditions give a chance of spawning monsters. For now, I'm working on fear conditions (shaken, frightened, panicking, and cowering). I was thinking about basing the monsters that would form from fear off the eidolon tables (eidolon level = affected creature's level/CR + inverted Wis?/normal Cha? modifier). If I go this route, I'll figure something out for eidolons over level 20. Either way, I think that these monsters should have either a Sanctuary effect against the creature that manifested it (the creature suffering from the fear condition, not the one that inflicted it), or an ability that prevents the creature that manifested it from recovering form their fear condition. Any suggestions?
Maybe develop a new spell?
The random eidolons are pretty complicated, perhaps a creature built around the feared creatures fears?
I'm going to have it be possible to manifest a nightmare creature from being confronted by a phobia or through a spell I'll make. I'll just make a template to apply to creatures to turn them into nightmare manifestations.
How about the spell is from the illusion school (Will save to disbelieve, failure gives a fear condition and forces a second Will save to prevent a nightmare from manifesting)? Any ideas?
What should I do for the template?
I think there's a few things you can do:
* Have fights that didn't actually happen. This can be done a bit like Eternal Darkness; where the world starts shifting in ways that it actually isn't because your brain is not quite right.
* Have horror elements that didn't happen that don't make sense (knocks on doors or windows, especially if they don't exist.) Have doors or windows appear when they didn't exist before, etc.. and the interaction with these things should get fundamentally weirder the more you go into them.
I'm a fan of (when using fear descriptions) trying to get the player to run via descriptions of what is causing the fear. Maybe "The <monster>'s hands seem to be holding black holes sucking the light around them; you have heard of such spells and are sure it would result in certain death. Tendrils from this black mass reach for you and the world starts going dark."
A player getting that description will adequately not only understand they're about to die, but will tell that to the other players. Those that pass the save may have a different belief about the situation; but that type of save is a good "roll behind the shield" roll; as it's anyone's guess whether they're being fooled by something that will kill them, or fooled by something that won't.
Those sound like awesome option, but how am I going to give them different sets of info that contradict each other without them thinking that I'm making continuity errors?
So I've been thinking about this a bit and I think what I'll do is have the other players (potentially) act out what they're doing without knowing; and then retcon things so that all the players get to participate, but it was really all in the mind of the player affected.
As in:
* dude who is going nuts fails a check or has a nightmare
* the entire party participates and reacts as they would normally
* at some point he exits the nightmare
* The GM retcons some amount of the happenings (or all of them) and it is now apparent that it didn't really happen.
* You might consider damaging one of his Mental Ability Scores on some check with these; but that's debatable
This keeps everyone playing and it doesn't break the hallucination until it actually breaks, and the players don't know if it's real or false. Even better, it means that some of the crazy things you put in your campaign that seem like nightmares will catch people off guard haha; which is really what you're trying to do by breaking the continuity of the session with the retcon style.
I've only been thinking about this a couple hours, so this advice may change!
EDIT: If the whole party is susceptible, this can potentially leave some of the happenings that are strange in place; with the GM preferably knowing which ones are real (so he doesn't goof the story) and the players being left guessing sometimes if that person they encountered really existed.
EDIT 2 (moments later!): I think I'll try this this weekend. One of my players has accidentally been mildly corrupted, and I think having a really unexpected battle with an NPC that turns out it didn't happen will be awesome.
FINAL EDIT I SWEAR: Just to say; I've built some nightmare (well.. Eldritch) creatures from Eidolons. They work really well. One is based on an old Chaos Spawn (40k) and it functions how it looks; except that it's "large" a couple levels too early... but that's alright.
Those sound like awesome option, but how am I going to give them different sets of info that contradict each other without them thinking that I'm making continuity errors?
If you sarcastically say,"Oh yeah, I forgot about that." it will really mess with them.
But seriously, if you take the basic dream or nightmare monster(both in the bestiaries) and advance them with the eidolon evolutions, you're in business.