In a fantasy world of magic and monsters, even things as mundane as race and gender can see fantastic variations. The degree to which fantastic genders appear, and their place in society, can significantly impact the D&D world. Those DMs who decide to include fantastic genders should give serious thought to their place in the world and its civilizations. The hermaphrodite gender, a few fantastic sexual characteristics, and a few notes on cultural/social considerations (as well as a few default answers to them), will be outlined below.
Note: One should not unilaterally elect to include fantastic genders, or show up to a game intending to play a fantastically gendered character without warning. Like all content that is intended for mature sensibilities, one should discuss this with the DM, and other players, to ensure that it's inclusion does not cause discomfort among the gaming group; remember, the ultimate goal is for everyone to have fun.
Hermaphrodites are persons who possess a mix of both male and female sexual characteristics (primary sexual characteristics are those used for reproduction; secondary characteristics differentiate the genders but are not used for procreation). Unlike in the real world, fantasy hermaphrodites may possess fully developed and functional traits from both genders.
The most common hermaphrodites in fantasy are those who possess the secondary characteristics of one gender, while having the primary characteristics of the opposing gender, or of both genders. It's rarer for hermaphrodites in fantasy to possess a mix of secondary characteristics. This is attributable to the fact that a person's secondary characteristics often dictate how a society interacts with them (see fantastic genders in society).
Aberrant Sexual Characteristics
At times, the fantasy world of D&D sees wild variations in sexual characteristics. Whether this is the result of biology, magic, an unusual heritage, or the influence of the far realm; these variations come in four general varieties.
Mythic Fertility: Affects only those having female primary sexual characteristics. Like the queen who birthed the minor of Greek myth, the character's ability to procreate is not limited by race or species.
Polymastia: Affects only those with female sexondary sexual characteristics. The character has one or more additional (and perhaps fully functional) mammary glands (i.e. breasts).
Polyphalia: Affects only persons with male primary sexual characteristics. The character has one or more additional (and perhaps fully functional) phallus.
Zoomorphia: Can affect persons regardless of their sexual characteristics. The character has one or more primary or secondary sexual characteristics that are (in form and in function) like those of an animal or monster.
Fantastic Genders in Society
Secondary sexual characteristics, being used to differentiate gender, will usually dictate what gender role a fanstastically gendered person is expected to play according to their culture. Since the default for D&D cultures is equality between men and women, people are regarded as equals regardless of what secondary characteristcs they possess.
Meanwhile, aberrant sexual characteristics are often attributed to a magic effect (often a curse) or to the character having some kind of mixed heritage. A few cultures, particularly those who are more in touch with nature, may ascribe a religious significane to them or may cast them out as being "unnatural" creatures.
If a DM who includes fantastic genders chooses to stray from the default equality of D&D, it becomes necessary to consider such things as marriage rights/customs, parental rights, and whehther or not the fantastically gendered are second-class citizens or are put upon a pedestal. What do the various civic, criminal, military, and religious orders think of such people? Are they allowed to be ordained into the clergy? Do they live in segregated housing? This is but a sample of the questions raised b the inclusion of fantastic genders.
DM's Note: As one can see from the previous questions, how a fantasy culture treats the fantastically gendered can provide a nice allegory for plot lines that involve discrimination, segregation, and human rights. If the fantastically gendered have become this way because of a reason beyond their control, they can also be used to tell stories related to refugees, distaster victims, the deformed, and even the mentally ill. Not everyone enjoys such heavy themes, which is one of the reasons why the inclusion of fantastic genders should be discussed with one's gaming group.