This was the history that I thought up for the shadow figure:

His name was Nathan before he was killed, and he grew up with a great attachment to pokemon. He became an excellent pokemon researcher and spent most of his time out in the forests. While trying to study pokemon in their natural habitat, where the mansion is built, Nathan was attacked by a group of pokemon poachers. Using his tag team effort with his best friends a Machoke and a Gardevoir, Nathan managed to beat the poachers. After Officer Jenny took the poachers to jail, Nathan went back to his research once again. However, a couple of weeks after the incident, an organization of professors who claimed to be is great colleges asked Nathan to join them. Believing that it was for the benefit of all, Nathan accepted the job. Yet, during the course of eight months, Nathan found that the researchers were actually trying to close the door to pokemon’s hearts and make them into fighting machines. They had actually been working in cohesion with the poachers to try and get the best pokemon available. Trying to stop the group, Nathan was defeated by the numbers of researchers, and in the aftermath, he was shot by the beam that turned pokemon into fighting machines. Having his heart closed, Nathan became a heartless serial killer killing pokemon and humans alike. However, inside his own mind, Nathan was trapped and forced to watch himself do harm to everyone and everything. Finally, the Machoke and the Gardevoir, in a last ditch effort to save their master, were forced to take the life of their master. Thankful, and yet dually vengeful, Nathan’s spirit remained torn and corrupted leading him to haunt and show people their worst fears.