Sex and magic in Rothganar are inextricably linked. The pleasure a caster feels when they perform a working is often likened to sexual pleasure, and many come to prefer it.
There are very few active practitioners of sex magic. It’s not something taught to children, as one might imagine, and great care is required in the practice. Otherwise, something can break, usually the aura of the participant(s) being drawn from, but in extreme cases, both.
Sex magic functions by allowing one to draw power through another’s aura, adding temporary strength to their own castings. Consensual contact is the most useful for this sort of practice, but some unscrupulous casters have been known to force themselves on others for the purpose of gaining magical power.
Witches are particularly valuable for this practice, because they can be drawn from directly, and without interference their auras replenish with power quickly and easily. The limits of a caster’s aura when drawing from the planet don’t affect them when drawing from a witch; instead, the aura of the witch herself is the only limit. In the case of Mongo the Great, for example, Mongo and his illusions on their own weren’t particularly great. He’d simply found a witch and was using her to feed his aura.