My campaign isn’t as suggestive or dream-like as many others; it’s in all honesty pretty bog-standard fantasy, although the frequency of monsters (humanoids especially) is dialed down a lot, inspired by LotFP’s philosophy of keeping things strange.
Recently, however, I’ve begun introducing the more philosophical thought that adventurers and other bizarre fringe-creatures really are explorers of the “beyond”, that there’s something outside civilization which they dive into. It could be that “mythic underworld”, it could be the Fae encroaching on reality, but they go where sane people wouldn’t. And they also go places which civilization would rather see not exist at all, into the badlands, deep forests and dismal swamps.
This adds a more suggestive feel to the classic “murderhobo”, they really are to be feared, not just because they are violent and follow their own strange morals, but because they enter the unknown, and who knows what they’re bringing back? The local peasants have been leaving offerings to the swamp hags for centuries, and apart from the occasional lost child there’s never been a problem. They don’t need the hags killed, and the definitely don’t need the hags angered.
It also explains the PC’s powers and abilities; they have a touch of the fantastic on them, the mythical, and so they can access abilities and secrets beyond those who are afraid to upset the balance.
So far I haven’t really considered if this should influence game-play or mechanics. It somehow feels like it shouldn’t have to, that D&D is written to reflect exploration of this Beyond. It’s interesting to consider that, at least to me, D&D is weakest as a system once it instead seeks to model the “real” world, the mundane world of peasants and kings, harvests and taxes. Who needs it? Give me a carousing table, an equipment list and a list of hirelings stupid or desperate enough to be willing to venture out beyond civilization, and then let’s head into adventure again…
One consequence, at least in my campaign, has been making the guardians of civilization more powerful, not less. Veterans have 2 HD, and knights have 3 HD, many NPC clerics are rather high level. They’re the strongest champions of the “normal”, the bulwark against dragons and undead and old gods; they should be powerful, although predictable and rarely in opposition to the PC’s unless they’re very actively spreading chaos in the lawful parts of the world. They are, to some extent, the future, the inexorable advance of civilization as it pushes the Beyond and claims new lands.
I was worried that this might be a bit boring and predictable, but instead I find this trope is really helpful in play. My players hate the tax-men, bishops and barons who interfere in their work, and as they grow more powerful they become more and more of a threat to the established order, as criminals, rebels, “false” prophets and renegades. It generates conflict and flux – in other words, fun!