Ghostly Mysteries (Danny Phantom/Gravity Falls crossover)

The closer they get, the more they can see. A head of black hair, blue jeans, a white t-shirt, pale skin... but something isn't right. Dipper strains his eyes until the figure shifts, visibly contorting in pain even as it seems asleep. That's when Dipper and Mable get a proper look at him.

The figure is a human boy, probably a teenager, and he was covered in blood.

a rewrite of Uhh...Boo?? Five years later :)