Shark is Finn's older cousin, and they rarely see each other due to the fact they're super Adventurers. But when they were kids they would run around with wooden swords and fight plants.
Shark is also a Shapeshifter, so she can change forms at will; although Finn didn't know that either. Shark is fast, agile, lean and fit for any challenge thrown at her.
Schivies has been Shark's partner since they were children. Schievies is magic also, and he can grow, shrink, or do most anything you can imagine. He knows most things about the Land of Oo and most rulers, monsters, and a bunch of things about the land.
The Gnome King is known for being too overconfident and having a cocky attitude. He thinks he can do all this awesome stuff; but really, he's just a wuss. Shark saves him on a daily basis, and in return? Nothing.
The Germcaster is the cause of any virus you come down with. He can go through things and become invisible so you never see when he zaps you with whatever you get sick with. Shark hates getting sick; so whenever she sees him trying to make others sick; she beats him up.
Aaaaand those are my OC's! ANYONE WHO LIKES ADVENTURE TIME SHOULD DO THIS... NOW.