Lycanthrope

One of the most ancient and feared of all curses, lycanthropy can transform the most civilized humanoid into a ravening beast. In its natural humanoid form, a creature cursed by lycanthropy appears as its normal self. Over time, however, many lycanthropes acquire features suggestive of their animal form. In that animal form, a lycanthrope resembles a powerful version of a normal animal. On close inspection, its eyes show a faint spark of unnatural intelligence and might glow red in the dark.
Evil lycanthropes hide among normal folk, emerging in animal form at night to spread terror and bloodshed, especially under a full moon. Good lycanthropes are reclusive and uncomfortable around other civilized creatures, often living alone in wilderness areas far from villages and towns.

Curse of Lycanthropy

A humanoid creature can be afflicted with the curse of lycanthropy after being wounded by a lycanthrope, or if one or both of its parents are lycanthropes. A remove curse spell can rid an afflicted lycanthrope of the curse, but a natural born lycanthrope can be freed of the curse only with a wish.
A lycanthrope can either resist its curse or embrace it. By resisting the curse, a lycanthrope retains its normal alignment and personality while in humanoid form. It lives its life as it always has, burying deep the bestial urges raging inside it. However, when the full moon rises, the curse becomes too strong to resist, transforming the individual into its beast form — or into a horrible hybrid form that combines animal and humanoid traits. When the moon wanes, the beast within can be controlled once again. Especially if the cursed creature is unaware of its condition, it might not remember the events of its transformation, though those memories often haunt a lycanthrope as bloody dreams.
Some individuals see little point in fighting the curse and accept what they are. With time and experience, they learn to master their shapechanging ability and can assume beast form or hybrid form at will. Most lycanthropes that embrace their bestial natures succumb to bloodlust, becoming evil, opportunistic creatures that prey on the weak.