No, not as in supernatural beings. As in the supporting cast of Bishoujo Senshi Sailormoon! They are personally one of my very favorite aspects of the series. You know you love them. So here they are!
Luna, Artemis & Diana
Before Mamoru knew that Luna could talk, he was still good to her. Luna was once crossing the street, deep in thought. She didn't realize that a bus was about to hit her. Mamoru leapt into the street, grabbed her and dodged out of the way just in time - much like Kakeru would do later in the Sailormoon S Movie. Usagi didn't even ask Mamoru why he had Luna and immediately yelled at him to leave her cat alone. Poor guy. In Sailormoon R when Mamoru is trying to avoid Usagi, Sailormoon is unconcious and a cardian is draining away energy from within her. No one can wake her up - but Luna knows that Mamoru can. She races off to Mamoru's apartment and leaps in through the window onto Mamoru's stomach, waking him up. She orders that he come before Sailormoon dies. "You and Sailormoon were in love once...why are you so cruel to her?" she asks. Mamoru can't answer her. "Because..." Luna becomes impatient. "Hurry up! Or she'll die.." In later seasons like SuperS, Mamoru seems to be the most reliable one to discuss senshi matters with, because he isn't easily distracted like the girls are. I think Mamoru is seen hanging around with the moon cats the most in the SuperS season.
Artemis is the closest thing Mamoru has to a guy companion in terms of those involved with senshi matters. We aren't given any special extra anecdotes about Mamoru and Artemis, but they seem to converse freely and in episode 133 Mamoru gave Artemis some advice after he made Luna angry. They seem close enough and again, are able to discuss senshi business more seriously.
Just like Chibiusa is the future daughter of Usagi and Mamoru, Diana is the future daughter of Luna and Artemis. In the anime she doesn't appear until the SuperS season, and is very mannered. She calls Mamoru and Usagi "Sir" and "Madame", even after Mamoru says it's all right to call him "Mamo-chan". She can't help but treat them as the royalty she knows they are in the future. Mamoru seems to really like Diana and totes her around a lot. Diana often speaks about what the King and Queen are like in the future.
Motoki is the first friend of Mamoru's that we meet. They seem to know each other pretty well. In the first season,they are complete opposites in terms of Usagi. Motoki is gentle and nice to Usagi, and Mamoru...well, we have "Odango Atama" to show for him. I still believe that Mamoru teases Usagi because he likes her. I don't know...I always thought it was kind of obvious. I also always thought that Motoki sorta knew this. Mamoru and Motoki attend the same college, Azabu Institute of Technology. But there's one big loophole with their friendship in the anime (mainly for plot's sake I think), after Mamoru is brainwashed by the Dark Kingdom and resides with them during this period - Motoki doesn't seem to notice his absence. But he's so nice, so we'll forgive him.
Unazuki is Motoki's younger sister, and we are introduced to her in Sailormoon R, in the Black Moon arc of the storyline. We meet her on kind of an akward basis - Mamoru is trying to stay away from Usagi to protect her. Usagi spots Mamoru giving Unazuki a ride home. She inquires about who she is and Mamoru rather coldy responds, "None of your business." Ouch! It turns out that he was just giving her a ride home and nothing more. She's a very sweet person and confides in Usagi when she wants to talk about things like her boyfriend. She appears throughout the R, S and SuperS seasons.