The following is backstories and descriptions for OC's I've created, or characters such as Shadow Mario who have a completely different backstory than the canon series. If the backstory only applies to one story, as well as anything that has not been revealed about the character in a story, shall not appear here.
Shadow Mario - *Updated on 4/16/2013* - (The following backstory originates from 'Rising Shadows' and applies to most, if not all of any fanfics involving the character.) Any information on Shadow Mario prior to 'Super Mario Sunshine' is not yet known to anyone besides TheFollyWriter, but will be released soon enough. During the events of 'SMS', Shadow Mario found himself on Isle Delfino, with all the memories of Mario, and he believed that our Mario was actually a poser, who had somehow managed to steal his identity. After deciding to team up with Bowser and his son to take down the fake, he received a special handkerchief from Kamek, letting him switch places with Bowser Jr at any given time. He quickly "saved" Princess Peach, helping to keep her away from the villain (aka Mario) for the rest of the game. After being thwarted, he soon took refuge in Twilight Town, hiding in the Creepy Steeple and taking the name Doopliss before covering himself in a sheet and various other party items, attempting to block out "his" past. After a few years of simply reading, learning various new abilities, and pranking the villagers in hopes of receiving attention and friends, Shadow Mario was just about ready to give up. However, during his final prank, he once again encountered Mario, able to use his new found abilities to switch roles with the plumber. Although he was soon put back in his place, this gave him a taste of what it was like to be the hero again, and so he began following Mario, hoping to learn all about him before engaging him in battle, (he says his time with the Shadow Sirens was 'to creepy to talk about'). Even though he followed him into space twice, and then through another adventure through the Mushroom Kingdom, he changed his appearance both times and didn't let Mario know he was gathering information. Feeling prepared, Shadow Mario took Peach as bait, saying it would make Mario try his best in the battle he challenged him to, in which the winner would be proven as "the real Mario".
Charlie - *Updated on 4/16/2013* - (The following backstory originates from 'The Hardest of Jobs', and there is no guarantee this character will be used again...ever) Charlie is a hill in the background of one of the Mario stages, watching. He's been watching since before the Mushroom Kingdom was known as the Mushroom Kingdom, but he is not able to communicate in any way shape or form, and is stuck to thinking to himself 24 hours a day, 7 days a week. He does not eat or sleep, and he assumes he will live forever, because he doesn't see how a hill can die.
Olive - *Updated on 5/14/2013* - (Olive does not have an official backstory thus far, but appears in "Moves") Olive is the daughter of Mario and Peach. She has dark brown hair, a light blue denim dress with a red undershirt. Ever since she was little, she's adored her father. She frequently takes her father's spare hats (or even the one he's wearing at the time). Finally, she managed to beat the odds of her parents, and end up with green eyes.