(Supernatural) Want to learn a Gift, Rite, or something equivalent to your supernatural species that no one else on the MUSH has? For Garou characters, Mentor represents an NPC Garou of rank equal to whatever the Mentor background is at, who can be contacted and is usually amenable to teaching your character.
Other supernaturals (Vampires, Mages, Bete) should contact the appropriate sphere wiz for more details as it pertains to you.
The Mentor character should be written up briefly and included in your characters &GMINFO (see "+help gminfo"). In a pinch, Mentor can sometimes serve as 1 point of Contacts exclusively for limited types of information elsewhere in the world. It's more like half of a point of Contacts.