If, in D&D, superstition is always right, then cultural taboos are to be doubly respected. Many of the magical ills in the D&D universe arose because someone violated a taboo.
When someone violates a taboo, have them make a saving throw. If they fail, they may contract the curse appropriate to their crime.
cannibalism: If you eat of your own kind, you’re likely to contract a disease that causes your hair to fall out, your flesh to whiten, and your teeth to hunger for more human flesh. In the disease’s final stage, you become a ghoul, and you will spread your disease to those you kill. Let that be a lesson to you: if you’re stuck in a cave-in, the human should eat the elf corpse and vice versa.
murder of kin: The curse attendant on brother murdering brother is attested in one of the oldest sword and sorcery tales of all: the story of Kane, by Karl Edward Wagner. Just kidding. But seriously, kin killing should put you magically outside the pale of society. I’d say that someone who contracts the Kin-Killer’s Mark can’t recover healing surges by sleeping in a settlement, and takes damage, instead of healing, from clerical healing from allies. I wouldn’t be surprised if kin-killing were a necessary part of becoming a death knight, as well.
murder of guests: When you share food with someone, you enter a guest-host relationship in which violence is forbidden. Those who violate this rule are doomed to lose food’s sustaining powers: from now on, they can only sate their hunger with violence and betrayal – in other words, human blood. They become vampires. Consider also vampires’ inability to enter a house without permission: the vampire is constantly forced to enter an explicit guest relationship, and then betray it in a bloody feast, re-enacting the vampires’ initial betrayal of the guest meal.
bestiality: D&D is a world where every monster is half this and half that (or a third!) and it can’t all be the work of mad wizards. Obviously, in D&D, any mating can produce offspring: furthermore, I think that not only will the children be beast-men, but the guilty parents may take on bestial natures as well. This is especially common near the feywild, where every animal species’s nobility can take human form. However, not every satyr goat-herd has the excuse of living near the feywild.
incest: This taboo is most commonly violated by royalty, so much so that its visible effects are often called the King’s Curse. It not only enters the bloodline but affect the parents. The King’s Curse manifests as madness and cruelty. It also often causes extreme physical delicacy (a penalty to fortitude defense).
What about taboos like exposing your ankles in Victorian England, or not keeping kosher? Do they only affect people who believe in them? Is it OK for me to wear flip flops???
I’d think that the point of this exercise would be blunted somewhat if taboos “only affect people who believe in them”. D&D is full of folk beliefs turned into objectively real forces: magic, ghosts, werewolves, etc., and this proposal is just extending that to taboos. A D&D character doesn’t have to believe in werewolves to be attacked by one. Similarly, I’d assume that a character doesn’t have to believe in or even know about the cannibalism taboo to fall prey to the ghoul curse. If the DM wants to run a game in the kind of setting where walking around with bare ankles would carry magical consequences, then I think it makes sense to apply those consequences to everyone.
That said, keeping kosher is a special case, because even in the real world, it’s usually not held to be a universal constraint, but rather, part of God’s covenant with His chosen people. So if you have Jews in your campaign setting, I think it would be reasonable to have tangible treif penalties for them and only for them. Although perhaps this could be covered under some sort of general system for handling oath-breaking.
And what about desecrating Temples?
Desecrating temples is interesting. Desecrating good temples is fairly straightforward, but what about evil temples? A paladin might feel morally obligated to wreck the shrine of Asmodeus, and poor the innocent maiden blood down the drain. Even if Pelor requires such an action, should the paladin be burdened with Asmodeus’s divine curse?
The most interesting answer here might be “Yes.”
Good stuff!
At first I was going to disagree with you on murdering kin and say that should be what turns you into a vampire, but it does work well with killing guests.
The most interesting aspects happen when the forces behind such things are personified. When you give the creator of the curse an AGENDA, then you have a potential adventure to pacify the curse-caster and thereby atone.
Oh! If you turn into a Vampire you should immediately acquire the Vampire class! That would be fun and would kind of work. I’d let them redo their attributes, feats, and skills however. They have to keep their race, which might mean they stop playing that PC. Could be a fun route if you get tired of being the party leader or defender!
If a player sneezes so does his PC. Quick, someone bless him before the Devil jumps in an replaces his soul!
I actually think that “all sneezes are in character” sounds like a good rule. From now on, whenever anyone refers to Rule 0, we all know that they really mean “All sneezes are in character.”
The DM should bring peppery food whenever the PCs are planning to try stealth.