I often like to throw in unique NPC’s who are the only member of their race / species. For instance, in a campaign that I was running about 12 or so years ago, I created a half-red dragon half-black dragon hatchling that was going to play a role in the entire campaign. You can download a PDF of the first adventure in the campaign (the only one I actually ran) on the resources page.
Currently, I am in the process of creating a drider-like NPC created from a human instead of a drow elf named a Spuman (spider-human). Since my post recently decrying the lack of pronunciation guides in Dungeons & Dragons, I felt that it is my duty to list my official pronunciation of the spuman: spyoo-man.
While I haven’t named him or her yet, I have come up with a back story. A human necromancer with an affinity for spiders became learned of Lolth and started to worship her. This priest was so devoted to Lolth that he or she spent most of their waking hours experimenting to create larger, smarter, more powerful spiders to conquer the world in the name of the Spider Queen. Because of this devotion, and the priest’s love of spiders, Lolth transformed the cleric into the first – and only – spuman as a reward.
There is not a significant difference in the role-playing aspect of a spuman versus a drider. Both have many abilities in common: venomous that can be used to poison their weapons, an improved movement rate due to the extra 4 legs, the ability to spin webs, etc. The only real differences are their appearance and their stats. The skin, hair, and eye color of a spuman looks like that of a human (which allows for a lot of variation) instead of that of a drow. Also, instead being black widow shaped like that of a drider, the lower portion of a spuman looks more like a wolf spider. The stats of a spuman are adjusted from a human base instead of a drow base as well.
In theory, there could be many spumans on different worlds. Or, the first spuman could teach the ways of Lolth to other humans who become transformed. In this way, it would be easy to populate a game world with clans of spumans to throw at the party, if you don’t like the idea of a one-off. Personally, I like the uniqueness of throwing a memorable NPC in front of the players, especially if they appear throughout the campaign.