D&D 3.0: Tales from Mystara
Some monks seek only enlightenment. Others are tempted by more shadowy pursuits.
The Ninja of the Crescent Moon is a mercenary clan whose members engage in sabotage and other covert missions for an outlandish fee – if the job meets their own inscrutable moral code. The ninja are a thorn in the side of both evil tyrants and just nobles, and no one outside the upper hierarchy knows what their real aims are. Their bases and safehouses are unknown to any outside the Crescent Moon, and would-be patrons contact them only through a long chain of contacts.
But once the Ninja of the Crescent Moon are hired, they generally complete the job by the next crescent moon (hence the name). The black-garbed ninja typically infiltrate their target, reveal themselves in a whirlwind of violence, then slip away into the shadows of the night.
Most ninja were once monks who heard the whispered promise of the ninja’s esoteric secrets. Curious, they began to research the Crescent Moon, following half-remembered rumors to their source. Any monk (or occasionally rogue or fighter) who manages to track the ninja back to their source are typically offered membership. Those who turn the Crescent Moon down are marked for death.
NPC ninja appear seemingly from nowhere, striking without mercy. They are often hired to steal a valuable item, kill a powerful rival, or infiltrate a besieged fortress as a precursor to an attack.