I don't know if this is interesting enough, but I thought about adding the vampire race. That is, drinking blood can be used as an aphrodisiac and weaken the victim or increase strength and experience without spending time in the library. Vampires or Werewolves are familiar legends and you can come up with a lot of things on them (silver, blood, mind control, etc.)
Sorry, I am writing from a translator, I am from Russia, and the English is not very good.